Hydrokinetic torque converter and lockup clutch therefor

ABSTRACT

A hydrokinetic torque converter is provided with a lockup clutch wherein the piston and other constituents of the lockup clutch are adequately cooled during each stage of operation of the torque converter and its clutch. The piston of the lockup clutch and/or the component which cooperates with the piston to transmit torque from the housing directly to the turbine of the torque converter is provided with a friction lining which establishes a portion of the path for the flow of fluid coolant between the fluid-filled compartments at opposite sides of the piston. The rate of fluid flow between the compartments is regulated by one or more adjustable valves which are carried by the housing of the torque converter and/or by the piston of the lockup clutch.

CROSS-REFERENCE TO RELATED CASES

This is a division of the now U.S. Pat. No. 5,782,327, patentapplication Ser. No. 08/649,065 filed May 16, 1996, which is a divisionof Ser. No. 08/272,920 filed Jul. 8, 1994, now abandoned.

BACKGROUND OF THE INVENTION

The invention relates to improvements in hydrokinetic torque convertersand to improvements in lockup clutches or bypass clutches for use intorque converters. More particularly, the invention relates toimprovements in torque converters of the type wherein a rotary housingis provided with a chamber for a pump, a turbine, a stator and a lockupclutch having an axially movable annular piston which divides thechamber into a first compartment and a second compartment. The chamberis filled with a suitable fluid (such as oil), and the piston of thelockup clutch carries a first friction surface which can be moved intotorque transmitting contact with a second friction surface when thelockup clutch is engaged. Still more particularly, the invention relatesto improvements in hydrokinetic torque converters and lockup clutcheswherein the first compartment is disposed between the piston and acomponent which carries the second friction surface, and wherein thepiston and/or the aforementioned component is provided with one or morepassages to establish a path for the flow of fluid from the secondcompartment substantially radially inwardly toward the rotational axisof the housing.

European Pat. No. 0 078 651 discloses a torque converter having a lockupclutch which includes an annular piston. That side of the piston whichfaces away from the friction surfaces is provided with channels servingto establish paths for the flow of fluid between a first compartmentwhich is bounded bound by a radial wall of the housing and the piston,and the second compartment which confines the pump and the turbine ofthe torque converter. The direction of fluid flow is from the secondcompartment into the first compartment so that the fluid can cool aviscous coupling which transmits torque between the piston and the hubof the turbine.

U.S. Pat. No. 4,969,543 (granted Nov. 13, 1990 to Macdonald for"Slipping Bypass Clutch Construction for a Hydrokinetic TorqueConverter") discloses a lockup clutch having an annular piston providedwith a first friction surface movable against a second friction surfaceprovided on a radially extending wall of the housing. The piston or thefriction lining on the wall of the housing is provided with channelswhich permit a fluid to flow from the second compartment into the firstcompartment within the housing even when the lockup clutch is engaged.The channels are provided at the same radial distance from therotational axis of the housing as the friction surfaces, the firstcompartment is disposed between the piston and the wall of the housing,and the second compartment accommodates at least the turbine of thetorque converter. The patentee desires to prevent excessive thermalstressing of certain parts of the torque converter such as could developduring continuous slipping of the friction surfaces during operation ofthe torque converter. More specifically, the patentee desires to preventexcessive thermal stressing of parts in the region of the two frictionsurfaces.

Published Japanese patent application No. 58-30532 also discloses alockup clutch or bypass clutch which is intended for use in ahydrokinetic torque converter and is provided with channels in theregion of its friction surfaces.

The aforementioned patent to Macdonald is but one of numerouspublications which propose the utilization of a lockup clutch whosefriction surfaces slide relative to each other in the disengaged as wellas in the engaged condition of the clutch. If the torque converter isinstalled in the power train of a motor vehicle, the slippage of thefriction surfaces forming part of the lockup clutch can be short-lasting(e.g., during shifting into a different gear) or such slippage can bemaintained practically within the entire operating range of the torqueconverter. The extent and the duration of slippage can depend upon thedesign of the prime mover which drives the housing of the torqueconverter and/or upon the selected gear ratio and/or upon one or morevariable parameters of the prime mover. The lockup clutch dissipatesenergy in the form of heat during slippage of its friction surfacesrelative to each other, and the quantity of dissipated energy can bequite pronounced (e.g., in the range of several kilowatts) duringcertain stages of operation of the torque converter. Such a situationcan develop, for example, when a vehicle pulling a trailer is drivenalong a mountain road, i.e., the torque converter is apt to dissipatelarge amounts of energy for an extended period of time. Moreover, whenthe slip clutch is engaged, the amount of dissipated energy can begreatly increased, at least for a short interval of time, i.e., thetorque converter and its lockup clutch are apt to be heated well above apermissible maximum temperature.

The purpose of the establishment of one or more paths for the flow of afluid coolant is to eliminate the aforediscussed drawbacks of heretoforeknown torque converters and their lockup clutches. A drawback ofheretofore known proposals to cool the lockup clutch of a torqueconverter is that the maximum torque which the lockup clutch cantransmit is insufficient, and this is attributable to certain dynamic orkinetic conditions which develop in the fluid flow. The ability ofconventional lockup clutches to transmit torque decreases in response toan increasing RPM of the housing of the torque converter as well as inresponse to increasing rate of fluid flow. This means that, if only thelockup clutch of a heretofore known torque converter is to transmittorque when the RPM of the housing rises to a preselected value, it isnecessary to increase the system pressure accordingly. This, in turn,renders it necessary to employ stronger parts, such as a stronger andbulkier piston as well as a higher-capacity pump. Furthermore, the rateof fluid flow per unit of time is then increased again which results inadditional losses.

The aforementioned reduction of the ability of the lockup clutches inconventional torque converters to transmit torque is attributable, amongother causes, to the development of forces generated as a result ofcertain dynamic conditions acting upon the radially inwardly flowingfluid in a sense to increase the fluid pressure. Such forces generate acomponent acting in the direction of the rotational axis of the housingof the torque converter so that the piston is urged to move in a senseto disengage the lockup clutch.

A further drawback of heretofore known undertakings to cool the torqueconverter in the region of the lockup clutch is that the flow of coolingfluid is overly dependent upon the temperature and/or viscosity of thefluid (such as oil) and/or the difference between fluid pressures atopposite sides of the piston. This means that, if a torque converter andits lockup clutch are constructed and assembled in a manner as proposed,for example, in the aforementioned patent to air Macdonald, theresistance to the flow of fluid in the channels between the twofluid-containing compartments must be selected to be satisfactory evenunder critical circumstances, i.e., the rate of flow of fluid whosetemperature has risen to a maximum possible or permissible value is lessthan the rate at which the system pressure in the torque converter woulddrop or collapse to an unacceptably low value. In the patented torqueconverter of Macdonald, the rate of fluid flow in the channels betweenthe two compartments at opposite sides of the piston of the lockupclutch is directly dependent upon the difference between the fluidpressures in the two compartments. Such pressure differential is thevariable parameter which controls the transmission of torque by thelockup clutch and, therefore, it cannot be resorted to for the selectionof the desired volumetric flow of the fluid. Thus, and in order tomaintain the losses in the torque converter above a minimum acceptablevalue, the rate of fluid flow must be low even when the differencebetween the fluid pressures in the two compartments rises to a maximumvalue, i.e., when the converter is called upon to transmit a maximaltorque. This may ensure a satisfactory rate of the flow of fluid coolantwhen the converter is called upon to transmit maximum torque but isunsatisfactory during transmission of lesser torque because thedifference between the fluid pressures in the two compartments of thetorque converter is too low.

OBJECTS OF THE INVENTION

An object of the present invention is to provide a novel and improvedtorque converter which is capable of transmitting large torques.

Another object of the invention is to provide a hydrokinetic torqueconverter which can transmit large torques without risking anoverheating of its constituents.

A further object of the invention is to provide a conveyance wherein thepower train embodies the improved hydrokinetic torque converter.

Still another object of the invention is to provide a torque converterwith a lockup clutch or bypass clutch which is constructed and assembledin such a way that it is adequately cooled in the region of its frictionsurfaces.

A further object of the invention is to provide a torque converterwherein the fluid is not overheated irrespective of the prevailingconditions.

Another object of the invention is to provide a hydrokinetic torqueconverter wherein the rate of fluid flow in the region of the lockupclutch is not only acceptable but rather highly satisfactoryirrespective of the circumstances of use of the torque converter and itslockup clutch.

An additional object of the invention is to enhance the exchange of heatbetween the parts of the lockup clutch in a hydrokinetic torqueconverter and a fluid coolant.

Still another object of the invention is to provide a lockup clutch orbypass clutch which is installed in a hydrokinetic torque converter andis constructed and assembled in such a way that the magnitude of torquewhich the clutch is to transmit can be selected and varied with utmostprecision. A further object of the invention is to provide a lockupclutch or bypass clutch which can be utilized in a hydrokinetic torqueconverter and is constructed and assembled in such a way that the extentof slippage between its friction surfaces can be regulated with aheretofore unknown degree of precision.

Another object of the invention is to provide a lockup clutch which canbe installed in the housing of a hydrokinetic torque converter andwherein the slippage between the friction surfaces can be selected witha view to satisfactorily compensate for surges and/or otherirregularities of torque transmission regardless of whether theirregularities are attributable to the prime mover which drives thehousing of the torque converter and/or to the power train between theprime mover and the housing.

An additional object of the invention is to enhance the comfort of theoccupant or occupants of a motor vehicle wherein the power train betweenthe prime mover and the wheels embodies a hydrokinetic torque converterand a lockup clutch or bypass clutch of the above-outlined character.

Still another object of the invention is to provide novel and improvedmeans for regulating the rate of fluid flow between compartments atopposite sides of the piston in a lockup clutch which is embodied in ahydrokinetic torque converter.

A further object of the invention is to provide novel and improvedpiston or pressure plate for use in a lockup clutch of theabove-outlined character.

Another object of the invention is to provide novel and improvedfriction linings for use in the lockup clutches of hydrokinetic torqueconverters.

An additional object of the invention is to provide a novel and improvedhousing for use in a hydrokinetic torque converter.

Still another object of the invention is to provide a novel and improvedlockup clutch or bypass clutch which can be utilized in a hydrokinetictorque converter and whose operation can be regulated to conform to oneor more variable parameters of the torque converter, of the means fordriving the torque converter and/or of means receiving torque from thetorque converter.

A further object of the invention is to provide a simple, compact andinexpensive torque converter and a simple, compact and inexpensivelockup clutch or bypass clutch for use in such torque converter.

Another object of the invention is to provide a novel and improvedmethod of establishing, dimensioning and orienting fluid flow permittingpassages and/or channels in the regions of the friction surfaces in alockup clutch or bypass clutch for use in hydrokinetic torqueconverters.

An additional object of the invention is to provide a lockup clutchwhich can be utilized in the above-outlined novel and improvedhydrokinetic torque converter and even in certain types of conventionaltorque converters.

Still another object of the invention is to provide a lockup clutchwherein the piston or pressure plate can perform one or more importantfunctions in addition to that of engaging and disengaging the clutch.

SUMMARY OF THE INVENTION

One feature of the present invention resides in the provision of ahydrokinetic torque converter which comprises a housing which isrotatable about a predetermined axis and is provided with afluid-containing chamber for the pump, turbine and stator of the torqueconverter. The latter further comprises a novel and improved engageableand disengageable lockup clutch or bypass clutch which is interposedbetween the housing and the turbine and comprises an annular pistonmovable in the chamber in the direction of the predetermined axis anddividing the chamber into a first compartment which is disposed at afirst radial distance from the axis and a second compartment. The lockupor bypass clutch (hereinafter called lockup clutch or clutch for short)comprises a first friction surface which is (directly or indirectly)carried by the piston at a second radial distance from the axis greaterthan the first radial distance and a second friction surface carried bya component which is rotatable with the housing. The first frictionsurface confronts and is in contact with the second friction surface inthe engaged condition of the clutch, and the piston and/or the componenthas at least one passage for the flow of fluid from the secondcompartment substantially radially inwardly toward the firstcompartment. The clutch further comprises first and second members whichdefine at least one channel serving to establish a path for the flow offluid from the at least one passage into the first compartment andwherein the fluid acts upon the first and/or the second member in thedirection of the predetermined axis. Still further, the clutch comprisesmeans for preventing axial movements of the piston in the direction ofthe predetermined axis in response to the action of the fluid in the atleast one channel. Otherwise stated, the first and second members arepropped or held relative to each other in the direction of thepredetermined axis in such a way that the power flow between them is anendless (closed in itself) flow.

The piston of the lockup clutch is preferably provided with at least onefriction lining and the first friction surface is then provided on theat least one friction lining. Furthermore, the first or second membercan form part of the piston, i.e., the piston can define the at leastone channel jointly with the second or first member. Otherwise stated,one of the first and second members can form part of the piston.

The orientation of the at least one passage can be such that itestablishes a path for the flow of fluid from the second compartmenttoward the first compartment.

The means for preventing axial movements of the piston in the directionof the predetermined axis in response to the action of fluid in the atleast one channel can include means for connecting the first and secondmembers to each other.

In accordance with a presently preferred embodiment, one of the firstand second members bounds a portion of the first compartment and isaffixed to the aforementioned component or to the piston, and the atleast one channel is then provided in the one member.

One of the first and second members can be rigid with (e.g., riveted toor of one piece with) the piston or the component.

The component can include or constitute or form part of a wall which, inturn, forms part of the housing and extends substantially radially ofthe predetermined axis. The first compartment is disposed between thewall and the piston, as seen in the direction of the predetermined axis.

The piston can be installed between a wall of the housing and theturbine of the torque converter.

If one of the first and second members forms part of the piston, the atleast one channel can be provided in the piston.

It is also possible to mount the first or second member on the piston,and the first or the second member can be disposed in the firstcompartment of the chamber in the housing of the torque converter.

The piston can be disposed in the housing between one of the first andsecond members and the first compartment.

The pump and the turbine of the torque converter are installed in thesecond compartment. One of the first and second members can divide thefirst compartment into two sections which are adjacent each other asseen in the direction of the predetermined axis.

At least one friction lining can be provided on the aforementionedcomponent and/or on the piston. The at least one passage is thenadjacent the friction lining, and such passage can be provided in thefriction lining.

The inlet of the at least one passage can be disposed at a first radialdistance from the predetermined axis, and the outlet of such passage canbe disposed at a lesser or shorter second radial distance from the axis.

The width of the first compartment (as measured radially of thepredetermined axis) can be selected in such a way that its exceeds thelength of the at least one channel. It is presently preferred to selectthe ratio of the width of the first compartment to the length of the atleast one channel in such a way that the length of the channel is notless than 50% of the width of the first compartment.

The at least one passage can constitute a cutout in, or is stamped orembossed into, the friction lining on or of the aforementioned componentand/or the piston.

The inlet of the at least one passage can extend substantially parallelwith the predetermined axis, and such inlet can be provided in theaforementioned component and/or in the piston. Furthermore, the outletof the at least one passage can extend substantially parallel with thepredetermined axis and can be provided in the piston and/or in theaforementioned component.

The at least one passage in the friction lining on the component and/oron the piston can be configurated in such a way that it establishes asubstantially meandering or zig-zag shaped path for the flow of fluid(e.g., oil) between the at least one channel and the second compartment.

If the piston is provided with at least one friction lining having afirst portion disposed at a lesser first radial distance and a secondportion disposed at a greater second radial distance from thepredetermined axis, the at least one passage can be provided in the atleast one friction lining in such a way that it has an inlet at leastclose to one of the first and second portions of the at least onefriction lining and an outlet which is at least close to the other ofthe first and second portions of the at least one friction lining.

The at least one friction lining of the annular piston defines therespective friction surface and can extend substantiallycircumferentially of the piston. The at least one passage can beprovided, at least in part, in the friction lining to extendsubstantially circumferentially of the piston and to define asubstantially meandering or zig-zag shaped path for the flow of fluidbetween the at least one channel and the second compartment.

If the at least one passage establishes a substantially meandering orzig-zag shaped path for the flow of fluid between the second compartmentand the at least one channel, the configuration of the passage is or canbe such that it includes at least two turns, i.e., the fluid flowingtherein is compelled to change the direction of flow more than once.

As already mentioned above, the piston can comprise or carry at leastone friction lining, and the respective friction surface is thenprovided on such friction lining.

The friction lining of the aforementioned component or of the piston isprovided with the respective friction surface, and such friction liningcan comprise or can be composed of at least two arcuate sections.

In accordance with another feature of the invention, the lockup clutchcan further comprise means for regulating the flow of fluid in the atleast one passage as a function of variations of at least one variableparameter of the torque converter. The arrangement can be such that theregulating means controls the flow of fluid in the at least one passagein dependency upon variations of at least one variable parameter of thetorque converter and/or as a function of at least one variable parameterof the means (e.g., a combustion engine in a motor vehicle) for drivingthe housing of the torque converter and/or as a function of at least onevariable parameter of the means for receiving torque from the turbine ofthe torque converter. For example, the torque converter can transmittorque to an automatic transmission in a motor vehicle.

The means for regulating the flow of fluid in the at least one passagecan constitute or include an adjustable valve which is installed at theinlet or at the outlet of the at least one passage. Such passage can bedefined by a suitably shaped portion of the aforementioned componentand/or the piston. The component can constitute a wall, and the at leastone passage (or at least one of plural passages) can be defined by asuitably shaped portion of such wall. For example, the at least onepassage can be provided in the annular piston, and at least oneadditional passage can be provided in the piston or in theaforementioned component (such as a wall of the housing).

The valve or any other suitable fluid flow regulating means can bedesigned in such a way that it includes means for regulating the flow offluid through the at least one passage to ensure that the rate of fluidflow through the passage is at least substantially constant within theentire operating range of the torque converter.

The pressure of fluid in the first compartment can differ or differsfrom the fluid pressure in the second compartment during at least onestage of operation of the torque converter, for example, when suchtorque converter is installed in the power train of a motor vehicle. Theaforementioned valve or equivalent means for regulating the flow offluid in the at least one passage is then designed to regulate the fluidflow as a function of differences between the fluid pressures in the twocompartments. The valve is designed to reduce the rate of fluid flow inthe at least one passage in response to increasing differences betweenthe fluid pressures in the two compartments.

If the valve is acted upon by centrifugal force in response to rotationof the aforementioned component and/or the piston, it is preferablyprovided with (or the lockup clutch further comprises) means for varyingthe rate of fluid flow in the at least one passage as a function ofchanges of differences between fluid pressures in the first and secondcompartments and at least substantially independently of the action ofcentrifugal force.

It has been found that the rate of fluid flow in the at least onepassage is quite satisfactory if such rate is different from the squareroot of the difference between fluid pressures in the first and secondcompartments.

Another feature of the invention resides in the provision of ahydrokinetic torque converter which comprises (1) a housing having afluid-containing chamber which is rotatable about a predetermined axis,(2) a pump, (3) a turbine and a stator in the chamber, and (4) anengageable and disengageable lockup clutch which is interposed betweenthe housing and the turbine. The clutch comprises an annular pistonmovable in the chamber in the direction of the predetermined axis anddividing the chamber into a first compartment and a second compartment.The clutch further comprises a first friction surface which is providedon at least one friction lining of the annular piston, and a secondfriction surface carried by a component which is rotatable with thehousing and serves to confront and contact the first friction surface inthe engaged condition of the clutch. The friction surfaces are disposedat a first radial distance from the predetermined axis, and the firstcompartment is disposed at a lesser second radial distance from suchaxis. The piston and/or the component is provided with at least onepassage for the flow of fluid from the second compartment toward thefirst compartment in the engaged condition of the clutch, and suchpassage is disposed at the aforementioned first radial distance from thepredetermined axis. The clutch further comprises a wall which isdisposed in the first compartment and extends substantially radially ofthe predetermined axis to define with a second wall at least one channelwhich establishes a path for the flow of fluid from the at least onepassage into the first compartment, and means for connecting the wallsto each other against movement relative to one another in the directionof the predetermined axis. The second wall preferably extends at leastsubstantially radially of the predetermined axis.

The second wall can form part of the piston, and the clutch can furthercomprise means for connecting the first wall to the housing againstmovement relative to the housing in the direction of the predeterminedaxis. Still further, the torque converter or its clutch can comprisemeans for connecting the first wall to the hub of the turbine so thatthe first wall is held against movement relative to the turbine in thedirection of the predetermined axis.

Still another feature of the invention resides in the provision of anovel and improved lockup clutch for use in a hydrokinetic torqueconverter and comprising a friction lining having at least one frictionsurface and at least one passage for the flow of a fluid coolant (e.g.,oil). The at least one passage is disposed at the at least one frictionsurface. The ratio of the thickness of the friction lining to theaverage depth of the at least one passage can be between 1.3 and 2.7.The depth of the at least one passage can be in the range between 0.2and 0.8 mm, preferably between 0.3 and 0.6 mm.

If the torque converter which embodies the improved lockup clutch isinstalled in a motor vehicle, the fluid coolant is or can be heated whenthe vehicle is in actual use, and the at least one passage is or can beconfigurated in such a way that it ensures the developement of aturbulent coolant flow at its inlet and/or at its outlet when thevehicle is in actual use.

The at least one passage of the improved lockup clutch can extend in thecircumferential direction of an annular piston which forms part of theclutch and carries the friction lining. The at least one passage canestablish for the fluid coolant a path which is an at leastsubstantially meandering or zig-zag shaped path, and the at least onepassage can have an at least substantially constant cross-sectionaloutline between its inlet and its outlet. The friction lining whichdefines a substantially meandering or zig-zag shaped path can have asubstantially circular shape.

If the improved clutch is embodied in a torque converter having at leastone variable operational parameter and being driven by a prime mover(e.g., a combustion engine having one or move variable parameters) totransmit torque to an automatic transmission or another torque receivingunit having one or more variable parameters, the clutch can be furtherprovided with means (e.g., one or more valves or flow restrictors) forregulating the flow of fluid coolant in the at least one passage as afunction of variations of at least one of the aforementioned parameters.

BRIEF DESCRIPTION OF THE DRAWINGS

The novel features which are considered as characteristic of theinvention are set forth in particular in the appended claims. Theimproved torque converter itself, however, both as to its constructionand its mode of operation, together with additional features andadvantages thereof, will be best understood upon review of the followingdetailed description of certain presently preferred specific embodimentswith reference to the accompanying drawings, wherein:

FIG. 1 is a fragmentary axial sectional view of a hydrokinetic torqueconverter and of a lockup clutch which embody one form of the presentinvention;

FIG. 2 is a diagram wherein the curves are characteristic of torquetransmission by certain conventional lockup clutches as well by theimproved lockup clutch;

FIG. 3 is a fragmentary axial sectional view of a modified torqueconverter and of a modified lockup clutch;

FIG. 4 is a fragmentary axial sectional view of a third torque converterand a third lockup clutch;

FIG. 5 is a fragmentary axial sectional view of a fourth hydrokinetictorque converter and a fourth lockup clutch;

FIG. 6 is an elevational view of a friction lining which can be utilizedin the improved lockup clutch;

FIG. 7 illustrates three arcuate sections of a modified friction lining;

FIG. 8 is a fragmentary axial sectional view of a further hydrokinetictorque converter and its lockup clutch;

FIG. 8a is a fragmentary axial sectional view of still another torqueconverter and of its lockup clutch which is provided with means forregulating the rate of fluid flow between the fluid-containingcompartments at the opposite sides of the piston or pressure plate;

FIG. 9 is an enlarged axial sectional view of the fluid flow regulatingmeans of the lockup clutch shown in FIG. 8a;

FIG. 9a is an axial sectional view of modified fluid flow regulatingmeans;

FIG. 10 is a fragmentary axial sectional view of a torque converter anda lockup clutch which is provided with differently positioned fluid flowregulating means;

FIG. 11 is a fragmentary axial sectional view of still anotherhydrokinetic torque converter and its lockup clutch; and

FIG. 11a shows a modification of the structure which is illustrated inFIG. 11; and

FIG. 12 is a fragmentary elevational view of a friction liningconstituting a modification of the friction linings shown in FIGS. 6 and7.

DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 shows a portion of an apparatus 1 which can be utilized for thetransmission of torque from a prime mover (e.g. the internal combustionengine of a motor vehicle) to one or more driven units, e.g., to thedifferential for the wheels of a motor vehicle. The apparatus 1comprises a torque converter 3 having a housing 2 which defines achamber for a pump 7, a turbine 10, a stator 12 and a lockup clutch 15.The torque converter 3 forms part of the power train and can beinstalled and assembled with other constituents of the power train in amanner as disclosed, for example, in FIG. 1 of U.S. Pat. No. 4,993,406granted Jan. 15, 1985 to Bopp for "Viscous Bypass Coupling For TorqueConverter". The disclosure of the patent to Bopp is incorporated hereinby reference.

The housing 2 of the torque converter 3 comprises two annular portionsor sections 4 and 5 which are sealingly secured to each other by awelded seam 6. Such seam is provided between the radially outermost partof the housing section 5 and an axially extending cylindrical part 4a ofthe section 4. The section 4 can receive torque from a rotary inputelement I of the prime mover, e.g., the camshaft or the crankshaft of acombustion engine. FIG. 1 shows that the radially inner part of asubstantially radially extending wall 9 of the housing section 4 isdirectly connected to the output element I; however, it is equallypossible to employ an intermediate part, e.g., a washer-like sheet metalconnector which is interposed and transmits torque between the outputelement I and the housing section 4. The radially inner portion of suchconnector is affixed to the output element I and the radially outerportion of the connector is affixed to the section 4 of the housing 2.Reference may be had, for example, to the aforementioned publishedJapanese patent application No. 58-30532.

The section or portion 5 of the housing 2 which is shown in FIG. 1performs the additional function of constituting the casing or shell ofthe pump 7. The vanes or blades 8 of the pump 7 are affixed directly tothe section 5. The turbine 10 is installed in the chamber of the housing2 between the pump 7 and the substantially radially extending wall 9 ofthe housing section 4. The radially inner portion of the turbine 10 isnon-rotatably affixed to or is of one piece with a tubular hub 11. Thishub is provided with axially parallel internal splines which alternatewith teeth and can receive the complementary teeth at the exterior ofthe rotary input element of a unit which is to receive torque from thetorque converter 3. For example, the hub 11 can transmit torque to therotary input shaft of a gear ratio box as shown in FIG. 1 of theaforementioned patent to Bopp.

The stator 12 of the torque converter 3 is installed in the chamber ofthe housing 2 between the radially inner portions of the pump 7 andturbine 10. The radially inner portion of the housing section 5 isconnected to or provided with a sleeve-like hub 13 which can berotatably mounted in the case of a transmission.

The aforementioned internal chamber of the housing 2 is shown at 14. Theleft-hand portion of this chamber receives the lockup clutch 15 which,when engaged, can transmit torque directly between the housing section 4and the hub 11 of the turbine 10. The lockup clutch 15 is designed andmounted in such a way that it operates in parallel with the torqueconverter 3. The chamber 14 further accommodates a damper 16 whichoperates in series with the torque converter 3 and can include a set ofarcuate coil springs or other suitable energy storing elements which cantransmit torque from the annular piston or pressure plate 17 of thelockup clutch 15 directly to the hub 11 of the turbine 10 when thelockup clutch is engaged. Reference may be had, for example, to U.S.Pat. No. 5,156,249 (granted Oct. 20, 1992 to Friedmann for "TorqueTransmitting Apparatus With Axially Deformable Primary Flywheel") whichis assigned to the owner of the assignee of the present application.

The piston or pressure plate 17 (hereinafter called piston or annularpiston) is installed in the chamber 14 at the wall 9 of the housingsection 4, and the radially inner portion of this piston has limitedfreedom of movement relative to the hub 11 of the turbine 10 in thedirections of the axis 27 of the housing 2. The piston 17 divides thechamber 14 into a first compartment 18 adjacent the wall 9 and a secondcompartment 20 which contains the pump 7, the turbine 10 and the stator12. The compartment 18 is disposed radially inwardly of the region 19 offrictional engagement of a friction surface on the piston 17 (and morespecifically of a friction surface on a friction lining 22 forming partof the piston) with a friction surface 21 which is carried by thehousing section 4. The two friction surfaces are caused to abut eachother in the engaged condition of the lockup clutch 15.

The friction surface 21 of the housing section 4 is provided at theinner side of a hollow frustoconical portion of the wall 9 radiallyoutwardly of the compartment 18, and the friction surface of thefriction lining 22 confronts the surface 21 in the engaged anddisengaged conditions of the lockup clutch 15. The two friction surfacestaper toward the axis 27 of the housing 2 in a direction away from thecompartment 20 and the parts 7, 10 and 12 therein. The friction lining22 is bonded or otherwise reliably secured to a hollow frustoconicalpart 23 of a disc-shaped member 24 which can be made of metallic sheetmaterial and is riveted (as at 17r) or otherwise reliably affixed to thepiston 17 so that the members 17, 24 are held against axial movementrelative to one another. The piston 17 is or can be obtained bydeforming a suitable sheet metal blank, e.g., in a deep drawing machine.

Recently developed torque converters are designed in such a way that thefriction surfaces of their lockup clutches can slip relative to oneanother in the disengaged as well as in the engaged conditions of thelockup clutches. This applies in particular for torque converters whichare installed in the power trains of motor vehicles. As alreadydiscussed hereinbefore, the ability of the friction surfaces of a lockupclutch to slip relative to one another in the engaged condition of theclutch (or at least during certain stages of operation of the motorvehicle) results in the generation of heat (i.e., dissipation of energy)which can be quite pronounced (e.g., in the range of several kilowatts).As also mentioned above, such situation can develop when a motor vehicleis coupled to a trailer and is driven along a mountain road. Stillfurther, the lockup clutch is likely to cause the torque converter togenerate large amounts of heat during engagement or disengagement of thelockup clutch. In addition to the aforediscussed patent to Macdonald,reference may also be had to German patent applications Nos. P 42 28137.7 and P 42 35 070.0-12 which also disclose torque converters withlockup clutches wherein the friction surfaces can slip relative to oneanother in the engaged condition of the clutch.

Excessive heating of the lockup clutch 15 could result in damage to ordestruction of the friction lining 22 and would also adversely affect atleast a substantial part of the supply of fluid in the chamber 14 of thehousing 2. In order to avoid excessive heating of fluid and of variousparts of the torque converter 3 and its lockup clutch 15 in the region(19) of the friction surface 21 and the friction surface of the frictionlining 22, the lining 22 is provided with one or more suitablyconfigurated and dimensioned passages 25 for the flow of fluid from thecompartment 20 radially toward the axis 27 of the housing 2, i.e.,radially inwardly toward the compartment 18 between the member 24 on thepiston 17 and the wall 9 of the housing section 4. The passage orpassages 25 (hereinafter referred to in plural) permit the establishmentof an uninterrupted flow of fluid coolant across the region 19 betweenthe friction lining 22 and the friction surface 21, even when the lockupclutch 15 is engaged or practically engaged. The rate of fluid flow inthe passages 25 of the friction lining 22 along the friction surface 21is sufficient to ensure the withdrawal of substantial quantities of heatfrom the housing section 4, from the piston 17 and from the member 24.

One presently preferred form of the passages in the friction lining of alockup clutch which embodies the present invention will be describedwith reference to FIGS. 6 and 7.

Each passage 25 has a inlets 26, 26a which are provided in the radiallyouter portion of the disc-shaped member 24 and through the piston 17,respectively. The inlets 26, 26a are aligned substantially parallel withthe axis 27 of the housing 2 to establish a path for the flow of fluidfrom the compartment 20 into the respective passage 25 toward thecompartment 18a. Each inlet 26a can constitute a bore or hole in thebody of the piston 17 and each inlet 26 can be a hole in a disc-shapedmember 24. The outlets of the passages 25 are located at the radiallyinner portion of the friction lining 22 and communicate with channels18a which discharge fluid into the radially inner portion of thecompartment 18.

The channels 18a are defined by two members of the lockup clutch 15,namely by the sheet metal disc-shaped member 24 and the adjacentradially inner portion of the piston 17. The path for the flow of fluidfrom the compartment 20 radially inwardly toward the compartment 18 isestablished in part by the passages 25 in the friction lining 22 and inpart by the channel or channels 18a between the piston 17 and the member24. Such path allows the fluid to flow from the compartment 20 towardand into the compartment 18 irrespective of whether the lockup clutch 15is engaged or disengaged. The flow of fluid from the passages 25 takesplace through openings or ports (e.g., bores) 28 in the member 24. Theradially inner portion of the member 24 is provided with impressed orembossed portions 29 which constitute distancing elements to maintainthe neighboring portions of the piston 17 and the member 24 at aselected distance from each other (as seen in the direction of the axis27 of the housing 2). The channels 18a alternate with the embossedportions 29 and are configurated in such a way that the fluid issuingfrom the ports 28 flows in the respective channels 18a substantiallyradially inwardly and into the compartment 18. The channels 18a can besaid to constitute a circumferentially incomplete annular space which isinterrupted by the embossed portions 29 of the member 24. The fluidwhich enters the compartment 18 (the latter is located between thecomponent or wall 9 of the housing section 4 and the sheet metal member24) is permitted to issue from the radially innermost portion of thecompartment 18 as indicated by the arrows. The discharge ends of thechannels 18a are located radially inwardly of the rivets 17r whichfixedly secure the neighboring portions of the members 17 and 24 to eachother so that the embossed portions or distancing elements 29 are urgedagainst the piston.

The piston 17 is provided with an embossed or impressed annular portion30 which is located radially outwardly of the channel or channels 18aand also constitutes a distancing element between the piston and themember 24. Such distancing element contributes to the rigidity of thepiston 17 and the member 24 in the region 19 of the friction surface 21and the friction lining 22. Furthermore, the distancing element 30establishes a radial seal between the members 17 and 24.

When the lockup clutch 15 is engaged, the flow of fluid coolant takesplace from the second compartment 20, through the inlets 26, 26a,through the passages 25, through the ports 28, through the channel orchannels 18a and thence radially inwardly toward the hub 11 of theturbine 10. The fluid which leaves the compartment 18 at the hub 11 iscaused to flow through a channel in the hub 11 and/or through one ormore grooves in or at the hub 11 to enter a heat exchanger (not shown)wherein the heated fluid exchanges heat with another fluid prior tobeing admitted into a sump, from where it reenters the compartment 20 inthe housing 2. In other words, the fluid coolant is caused to flow alongan endless path from the compartment 20, into the compartment 18(subsequent to cooling of the wall 9 at the friction surface 21 and ofthe piston in the region of the friction lining 22) to thereupon reenterthe compartment 20.

The piston 17 and the member 24 (i.e., the members which define thechannel or channels 18a) are connected to one another by the rivets 17r(which can be said to constitute or to form part of means for preventingaxial movements of the piston 17 in the direction of the axis 27 inresponse to action of flowing fluid in the channel or channels 18a) insuch a way that any axial component or components of the force generatedby the fluid in the channel or channels 18a are neutralized or taken upor counteracted by the member 24 so that the axial position of thepiston 17 remains unaffected by such forces. It is particularlyimportant that the aforediscussed axial component or components of theforce generated by cooling fluid in the channel or channels 18a shouldnot cause any axial displacement of the piston 17 in a direction to theright (as viewed in FIG. 1), i.e., in a direction to reduce themagnitude of torque which can be transmitted between the frictionsurface 21 and the adjacent friction surface of the friction lining 22.Otherwise stated, the members 17, 24 and the rivets 17r cooperate toensure that the member 24 and the piston 17 are propped or held relativeto each other in such a way that the power flow between these members isan endless flow, i.e., a flow which is closed in itself.

The just-outlined mode of causing the cooling fluid to prevent anoverheating of the wall 9 in the region of the friction surface 21and/or of the piston 17 in the region of its friction lining 22 withoutinitiating any undesirable reduction of the magnitude of torque which isbeing transmitted by the lockup clutch 15 is selected with a view totake into account the dynamics of cooling fluid flowing from thepassages 25, through the channel or channels 18a, and into thecompartment 18 at the hub 11 of the turbine 10. Furthermore, thisdistinguishes the improved torque converter 3 and its lockup clutch 15from the corresponding constituents of the apparatus which is disclosedin the aforediscussed patent to Macdonald. The patentee discloses atorque converter and a lockup clutch or bypass clutch which are designedin such a way that the forces which are attributable to the dynamics ofthe cooling fluid are free to initiate a rise of fluid pressure so thatthe upper limit of the magnitude of torque which can be transmitted bythe lockup clutch of Macdonald decreases in response to increasing RPMof the housing of the patented torque converter. A pronounced reductionof the maximum torque which can be transmitted by the lockup clutch ofthe patented torque converter is attributable to the dynamics of coolingfluid which flows in the patented torque converter radially inwardlybetween the radially extending wall of the housing and the piston. Themagnitude of maximum torque which can be transmitted by the lockupclutch of Macdonald decreases as the rate of fluid flow radiallyinwardly between the housing of the patented torque converter and thepiston of its lockup clutch increases. Applicants believe that this isattributable, at least in part, to the effect of coriolis accelerationupon the fluid which flows radially inwardly between the housing of thepatented torque converter and the piston of its lockup clutch. Suchacceleration develops in response to rotation of the housing of thepatented torque converter and tends to impart to the fluid coolant acirculatory movement, while the fluid flows radially inwardly, to thusincrease the pressure of the fluid coolant.

In contrast to the construction and mode of operation of the patentedtorque converter and its lockup clutch, the improved torque converter ofFIG. 1 is designed to ensure that any rise of fluid pressure whichdevelops as a result of radially inward flow of fluid in the channel orchannels 18a and which can generate or actually generates forces actingin the direction of the axis 27 cannot cause any axial shifting of thepiston 17 from that position which has been selected during transmissionof torque from the housing section 4 through the lockup clutch 15 and tothe turbine 10. At any rate, the influence of axially oriented forceswhich act upon the piston 17 and develop as a result of radially inwardflow of cooling fluid in the channel or channels 18a upon the axialposition of the piston is incomparably less pronounced (and actuallynegligible) in comparison with the influence of such forces upon theability of a conventional lockup clutch to transmit a desired torque. Inthe torque converter 3 and the lockup clutch 15 of FIG. 1, theneutralization of the aforediscussed axially oriented forces is achievedby the establishment of the connection (by rivets 17r) between themembers 17 and 24 which define the channel or channels 18a and cooperateto ensure that any force or forces developing in a direction to move thefriction lining 22 of the piston 17 axially and away from the frictionsurface 21 are counteracted by forces acting upon the member 24 in adirection to urge the friction lining 22 against the friction surface21.

The member 24 of the lockup clutch 15 shown in FIG. 1 extends radiallyinwardly close to the hub 11 of the turbine 10, i.e., the channel orchannels 18a are rather long (as measured radially of the axis 27).However, it is equally within the purview of the invention to replacethe member 24 with a member whose radially inner portion is locatedradially outwardly of the radially inner portion of the piston 17, i.e.,the radial length of the channel or channels 18a can be less, and evensubstantially less, than that of the channel 18a which is shown inFIG. 1. This may be advisable if the designer of the torque converter 3and its lockup clutch 15 desires to ensure that a predictable change ofthe magnitude of torque transmitted by the lockup clutch will take placein response to increasing RPM of the housing 2, i.e., in response toincreasing rate of fluid flow from the compartment 20 into thecompartment 18. It has been found that, at least in many or mostinstances, it is advisable to construct the lockup clutch 15 in such away that the length of each channel 18a (as measured radially of theaxis 27) is not less than 50% of the width of the compartment 18, i.e.,not less than 50 percent of the width of the piston 17.

It is further possible to modify the structure of FIG. 1 so that aportion of the fluid which is to cool the housing 2 in the region of thewall 9 and the piston 17 in the region of the friction lining 22 flowsfrom the compartment 20 into and through the channel or channels 18a andthe remaining portion of the fluid flows from the compartment 20 throughthe section 18b of the compartment 18, i.e., radially inwardly throughthat section which is disposed between the wall 9 and the member 24 (asseen in the direction of the axis 27). The channel or channels 18aconstitute the other section of the compartment 18. All that isnecessary is to provide one or more openings in the member 24 so thatthey permit the fluid to flow between the sections 18a and 18b of thecompartment 18. The combined area of the openings and/or their radialdistance from the axis 27 will be selected in dependency upon thedesired effect upon the cooling of certain parts of the torque converter3 and its lockup clutch 15 and/or upon the magnitude of torque to betransmitted by the lockup clutch during certain stages of operation ofthe improved apparatus.

In the diagram of FIG. 2, the RPM of the housing 2 is measured along theabscissa (at n), and the relationship M/Δp of torque which can betransmitted by the lockup clutch to the pressure differential of fluidat opposite sides of the piston is measured along the ordinate. Thecurve 31 denotes the relationship of transmitted torque to the RPM ofthe housing for a preselected constant pressure differential between thefluids at the opposite sides of a piston forming part of a conventionallockup clutch, namely a clutch which is designed to prevent the flow offluid between the spaces or compartments at opposite sides of thepiston. The curve 31 indicates that, if Δp is constant, the magnitude oftorque transmittable by the engaged lockup clutch in a conventionaltorque converter remains at least substantially unchanged. Torqueconverters utilizing such lockup clutches are disclosed, for example, inU.S. Pat. No. 4,649,763.

The curve 32 denotes in FIG. 2 the magnitude of torque which can betransmitted by the lockup clutch 15 in the torque converter 3 of FIG. 1in response to changes of the RPM and at a constant pressuredifferential Δp between the fluids in the compartments 18, 20 and whilethe fluid is free to flow from the compartment 20 into the compartment18 along the aforementioned path including the passages 25 and thechannel or channels 18a. Torque converters which include lockup clutchescapable of transmitting torque in a manner as denoted by the curve 32are disclosed, for example, in U.S. Pat. No. 4,445,599 (granted May 1,1984 to Bopp for "Cooling Means For Torque Converter Bypass") and inU.S. Pat. No. 5,056,631 (granted Oct. 15, 1991 to Macdonald for"Slipping Bypass Clutch Construction For A Hydrokinetic TorqueConverter"). The patents disclose lockup clutches wherein the piston(pressure plate) and/or the counterpressure plate is provided withchannels or openings disposed in the region of the friction lining orfriction linings and permitting fluid coolant to flow from a compartmentfor the pump and turbine of the torque converter into a compartmentbetween the piston and a wall of the housing of the torque converter.The establishment of a path for such flow of fluid in the patentedtorque converters entails that, when the value of Δp is constant, themaximum torque which can be transmitted by the lockup clutch decreasesin response to increasing RPM. This is due to losses of fluid in thepath or paths from the compartment for the turbine into the othercompartment as well as to fluid losses along the path from the othercompartment back into the compartment for the turbine. Additional lossesdevelop during fluid flow through the lockup clutches of the patentedtorque converters. The curve 32 indicates that, for a selected value ofΔp and at a low RPM, the maximum torque denoted by the curve 32 is lessthan the torque denoted by the curve 31. Furthermore, dynamic losses aresuperimposed upon the static losses so that the maximum torquetransmittable by a lockup clutch as denoted by the curve 32 is evenless. Dynamic losses are generated as a result of radially inward flowof fluid from the compartment for the turbine toward and into the othercompartment. This is also shown in FIG. 2 wherein dynamic losses causethe curve 32 to slope downwardly toward the abscissa when the value ofΔp is constant but the RPM of the housing of the torque converterincreases.

The broken-line curve 33 denotes in FIG. 2 the torque which is beingtransmitted by the improved lockup clutch 15 of the present invention ata constant value of Δp. It will be noted that the maximum value oftransmitted torque at a lower RPM and at a constant Δp is the same asthat denoted by the left-hand portion of the curve 32. However, themaximum transmittable torque (by the lockup clutch of the presentinvention) remains unchanged whereas the maximum torque denoted by thecurve 32 decreases due to pronounced influence of dynamic losses whenthe housing of the torque converter is rotated at a higher speed.

Of course, the characteristic curve denoting the maximum torque whichcan be transmitted by the improved lockup clutch 15 in the improvedtorque converter 3 of FIG. 1 can depart from the broken-line curve 33 inthe diagram of FIG. 2. For example, the maximum value of transmittabletorque may decrease at a certain rate in response to increasing RPM ofthe housing 2 of the torque converter 3. Nevertheless, it is nowpossible (by properly selecting the rate and the direction of fluid flowin the channel or channels 18a) to ensure that the curve 33 departs froman ideal curve solely as a result of static losses, i.e., that anydynamic losses developing when the lockup clutch 15 is in use do notaffect the maximum transmittable torque at a selected constant value ofΔp. At any rate, the influence of dynamic Δp losses upon thetransmission of torque by the engaged friction clutch 15 at a given Δpis nil or not more than a minute fraction of the dynamic losses whichdevelop when the transmission of torque is carried out by a conventionallockup clutch.

It is to be noted that the curves 31, 32 and 33 in the diagram of FIG. 2were plotted without taking into consideration certain other parameters,such as friction within the conveyed fluid and/or friction between theflowing fluid and the adjacent surfaces.

FIG. 3 illustrates a portion of a torque converter which embodies amodified lockup clutch 115. As can be seen in FIG. 1, the radiallyoutermost portion 17a of the piston 17 is adjacent the radially outerportion of the member 24. On the other hand, the radially outermostportion of the member 124 in the lockup clutch 115 of FIG. 3 extendswell beyond the radially outer portion of the piston 117 and includes arelatively short tubular or cylindrical part which is closely adjacentthe internal surface of the surrounding portion of the housing 102 ofthe lockup clutch. Furthermore, the radially innermost portion of thepiston 117 is not mounted on the hub 111 of the turbine for movement inthe axial direction of the housing 102. The member 124 is centered byand has limited freedom of axial movement relative to the hub 111. Itcan be said that the actual piston or pressure plate of the lockupclutch 115 of FIG. 3 is the member 124 and that the member denoted bythe character 117 serves as a reinforcement or stiffener for the member124.

The flow of fluid from the compartment 120 at one side into thecompartment 118 at the other side of the composite piston including themembers 117, 124 is indicated by arrows. Here, again, the fluid whichflows radially inwardly in the channel or channels 118a is compelled toact upon the members 117 and 124 (these members are riveted to eachother, as at 117r) in such a way that it cannot generate forces,whichwould reduce the ability of the clutch to transmit torque from thehousing to the turbine in the engaged condition of the clutch. Otherwisestated, the fluid which flows radially inwardly in the channel orchannels 118a cannot compel the piston 117 to move axially of and awayfrom the adjacent radial wall of the housing 102, i.e., in a directionto reduce the magnitude of transmitted torque in response to increasingRPM of the housing 102. Thus, the lockup clutch 115 is also capable ofat least substantially neutralizing dynamic forces which develop duringflow of fluid coolant from the compartment 120 radially inwardly towardand through the channel or channels 118a and into the compartment 118.Accordingly, the curve 33 of FIG. 2 denotes the torque which is beingtransmitted by the engaged lockup clutch 15 or 115.

As used herein, the term channel or channels is intended to embracediscrete grooves, tunnels or analogous path establishing recesses,bores, holes or cavities as well as circumferentially complete orincomplete chambers or spaces which enable the fluid to flow radiallyinwardly from the region of the friction lining or linings toward thesecond compartment 18 or 118. A circumferentially incomplete channel canbe composed of several individual channels which may, but need not,communicate with one another. Still further, the member 17 and/or themember 24 of FIG. 1, as well as the member 117 and/or 124 of FIG. 3, cancarry a set of discrete pipes or tubes which define the channels for theflow of fluid coolant from the passage or passages at the frictionlining 22 or 122 into the compartment 18 or 118. The radially innermostportions of the pipes can discharge the conveyed fluid directly into thecompartment 18 or 118 or into one or more channels or grooves in the hub11 or 111 wherein the fluid flows toward and through a suitable coolingsystem (e.g., one or more heat exchangers) and thence into a sump to bereturned into the compartment 20 or 120. Still further, it is possibleto provide one or more tubular members in compartment 20 or 120 todirect the fluid toward and into the passages 25 of the lockup clutch 15or into analogous passages of the lockup clutch 115.

The passages 25 in the clutch 15 of FIG. 1 and/or the passages of theclutch 115 need not necessarily be provided in the friction lining 22 or122. Thus, it is equally possible to provide such passages in the wall 9of the housing 2 of FIG. 1 and/or in the corresponding wall of thehousing 102. Still further, passages in the friction lining of a lockupclutch can be provided in addition to passages in the housing 2 or 102.

The construction of the clutch 115 is such that the member 117 need notbe provided with openings corresponding to the inlets 26a in the piston17 of FIG. 1; however, it is necessary to provide one or more openings(not referenced) in the member 124 of FIG. 3 in order to enable thefluid to flow from the channel or channels 118a into the compartment118. The openings 26 and/or the openings 28 and/or the openings in themember 124 can be designed with a view to influence the fluid in amanner corresponding to that of orifices of discrete nozzles. Forexample, the surfaces bounding such openings can be configurated tothrottle the flow of the fluid therein.

As already mentioned above, the friction lining 22 can be provided onthe wall 9 or this wall can carry an additional friction lining whichprovides the friction surface 21. Analogously the friction lining 122shown in FIG. 3 can be provided on the member 124 or on the adjacentportion of the housing 102, or the lockup clutch 115 can employ twofriction linings, one on the composite piston including the members 117,124 and the other on the adjacent radial wall of the housing 102.

Each friction lining can be bonded (e.g., adhesively secured) to therespective carrier. The passages in the friction linings can be formedby impressing them into the friction surfaces of the friction liningsand/or by removing some material from the friction surfaces.Furthermore, each passage (such as the passage 25 shown in FIG. 1) canbe provided in part in a friction lining and in part in the adjacentfriction surface, such as the friction surface of the wall 9 formingpart of the housing 2 shown in FIG. 1. It has been found that thepassages in the friction surfaces of friction linings and/or in thefriction surfaces which are contacted by friction linings when thelockup clutch is engaged ensure a highly satisfactory exchange of heatbetween the friction surfaces and the fluid coolant to thus ensure thatthe parts which are provided with friction surfaces as well as the fluidare not subjected to excessive or even very pronounced thermal stresses.

The provision of inlets (such as 26) close to the radially outermostportions of the friction surfaces and of the outlets (such as 28) closeto the radially innermost portions of the friction surfaces alsocontributes to highly satisfactory and uniform dissipation of heat bythe parts which carry the friction surfaces. The feature that thechannel or channels (18a, 118a) are relatively long (preferably not lessthan half the width of the compartment 18 or 118) is desirable andadvantageous because this even further reduces the likelihood of thedevelopment of unbalanced axial stresses which would tend to move thepiston of the engaged lockup clutch in a direction to reduce themagnitude of torque which is to be transmitted from the housing to theturbine of the torque converter.

FIG. 1 shows that the path of fluid from the compartment 20 into thecompartment 18 extends through the inlets 26, 26a of a passage 25 andthereupon through the respective outlet 28 which includes openings inthe friction lining 22 and in the member 17. However, it is equallypossible to extend the passages 25 all the way to the radially innermostportion of the friction lining 22 so that the establishment of an outletthen merely necessitates the provision of a hole or opening in themember 24 radially inwardly of the friction lining 22. In other words,fluid which issues from a passage 25 need not flow through the frictionlining 22 prior to traversing the member 24 on its way into the radiallyouter portion of a single channel 18a or one of several channels.

FIG. 4 shows certain details of a portion of a lockup clutch 215 whichis installed in the housing of a torque converter in such a way that thechannel or channels 218a are disposed between the piston 217 and themember 224 at that side of the piston which faces away from the wall 209of the housing. Otherwise stated, the piston 217 is installed betweenthe member 224 and the wall 209. The member 224 can constitute aconverted blank of metallic sheet material and includes a washer-likecentral portion, a frustoconical radially outer portion and asleeve-like radially inner portion. The passages 225 are providedbetween the frustoconical radially outer portion of the piston 217 andthe adjacent frustoconical portion of the wall 209. The outlet of eachpassage 225 communicates with the radially outer portion of a singlechannel 218a or one of several channels by way of a port 228 in thepiston 217. Each passage 225 is provided in the friction lining 222. Theradially innermost portion of each channel 218a communicates with theadjacent portion of the compartment 218 by way of one or more axiallyparallel openings 234 in the piston 217. It will be noted that thecompartment 218 extends radially of the axis of the housing of thetorque converter intermediate the wall 209 of the housing and theadjacent side of the piston 217.

Not only the channel 18a which is shown in FIG. 1 or the channel 118awhich is shown in FIG. 3 but also the channel 218a shown in FIG. 4 canconstitute an annular chamber extending all the way around the axis ofthe housing of the torque converter between the confronting surfaces ofthe piston 17, 117 or 217 and the member 24, 124 or 224. If the improvedlockup clutch is provided with a number of channels to establish pathsbetween the passages in a friction lining and the first compartment, themember 24, 124 or 224 can be replaced with one or more tubular memberswhich convey the fluid from the passages into the first compartment ofthe respective torque converter. By way of example, the member 24 ofFIG. 1 or the member 224 of FIG. 4 can be replaced with one or moretubes which establish paths for the flow of fluid from the passages 25or 225 into the compartment 18 or 218.

The outlets of the passages in a friction lining need not discharge thefluid coolant into a first compartment (such as the compartment 218) orinto a section (such as 18b) of the first compartment. Instead, theoutlets of the passages can discharge fluid into one or more radiallyextending bores in the hub of the turbine (such as the hub 11 of theturbine 10 which is shown in FIG. 1), and the hub then surrounds aconduit or other suitable means for conveying the heated fluid into aheat exchanger.

FIG. 5 shows a portion of a hydrokinetic torque converter 303 whichincludes a modified lockup clutch 315. The piston 317 of the clutch 315divides the chamber of the housing 302 into a first compartment 318 anda second compartment 320. The piston 317 is movable in the axialdirection of the housing 302 and is centered by the hub 311 of theturbine in the housing 302. A damper 316 is interposed between thepiston 317 and the turbine to transmit torque from the housing 302 tothe hub 311 when the lockup clutch 315 is engaged. The illustrateddamper 316 includes a set of arcuate energy storing elements in the formof coil springs, an input member which is of one piece with or iscarried by the piston 317, and an output member which is of one piecewith or is carried by the turbine or its hub 311.

When the clutch is engaged and the housing 302 of the torque converter303 is driven by a prime mover, such as a combustion engine in a motorvehicle, the fluid coolant is caused to flow from the compartment 320and at least substantially radially inwardly toward and into thecompartment 318. The fluid in the compartment 318 flows radiallyinwardly between the wall 309 of the housing 302 and the member 324which is affixed to the hub 311. The passages 325 at the friction lining322 have inlets 326 which are provided in nozzles 326a (one shown inFIG. 5) installed in and close to the radially outermost portion of thepiston 317. The illustrated nozzle 326a acts not unlike a flowrestrictor and the jet or stream of fluid issuing from its orifice 326(i.e., from the inlet of the respective passage 325) impinges upon thefriction surface 321 of the wall 309 forming part of the housing section304 as well as upon the friction surface of the friction lining 322. Theregion of the two friction surfaces is identified by the character 319and is disposed between frustoconical portions of the wall 309 andpiston 317. The passages 325 are or can be provided in the frictionlining 322 and/or in the friction surface 321 of the wall 309. Eachpassage 325 discharges the fluid directly into the radially outermostportion of the compartment 318, and such radially outermost portion canbe said to constitute a channel which directs the inflowing fluidradially inwardly toward the axis of the housing 302.

Even though the member 324 is nonmovably affixed to the hub 311 of theturbine while the piston 317 is free to move (within limits) relative tothe hub 311 in the axial direction of the housing 302, the fluid flowingradially inwardly within the compartment 318 cannot cause undesirableaxial shifting of the piston 317. This is due to the fact that any andall axially oriented components of the force generated by the fluid inthe compartment 318 are taken up by the member 324 which is affixed tothe hub 311 against movement in the axial direction of the housing 302.

In lieu of affixing the member 324 to the hub 311 of the turbine, it isequally possible to affix this member to the housing 302 in such a waythat the member 324 cannot move or cannot yield in the axial directionof the housing. All that counts is to ensure that the fluid flowingradially inwardly from the passages in the region of the frictionsurfaces toward and into one or more channels of or leading into thefirst compartment cannot cause any undesirable axial shifting of thepiston in a direction to disengage the respective lockup clutch or toreduce the magnitude of torque which is to be transmitted by the lockupclutch.

The passages can be provided in the friction lining on the piston of thelockup clutch, in the friction surface of the housing, in the pistonitself and/or even in the member which cooperates with the piston todefine one or more channels connecting the passages with the firstcompartment. For example, it is within the purview of the invention toprovide one or more passages in the member 24 of the lockup clutch 15 orin the member 124 of the lockup clutch which is illustrated in FIG. 3. Apiston which forms part of a lockup clutch or bypass clutch and isprovided with one or more passages for the flow of oil is disclosed inthe aforementioned U.S. Pat. No. 5,056,631 to Macdonald.

Those novel features of a hydrokinetic torque converter and its lockupclutch which were described with reference to FIGS. 1 to 5 can beembodied with equal or similar advantage in many other types of torqueconverters and lockup clutches. For example, the aforediscussed featureof causing the fluid to flow radially inwardly past the frictionsurfaces of the clutch and the provision of means for preventing axialmovements of the piston in the direction of the axis of the housing ofthe torque converter in response to the action of fluid in the channelor channels leading the fluid from the passages at the friction liningsinto the first compartment of the chamber defined by the housing can beput to use by properly modifying certain heretofore known torqueconverters, for example, those described and illustrated in U.S. Pat.No. 4,493,406 and in U.S. Pat. No. 4,445,599.

FIG. 6 shows a friction lining 422 which resembles a split ring and canbe put to use in the improved lockup clutch, e.g., in lockup clutches ofthe type described with reference to FIGS. 1 and 3 to 5. The frictionlining 422 comprises a continuous arcuate radially outer portion 422aand a continuous arcuate radially inner on central portion 422b. Thearcuate central portion 422b of the friction lining 422 is provided witha plurality of substantially meandering or zig-zag shaped passages 435in the form of cutouts or depressions in the friction surface, i.e., inthat surface which contacts the other friction surface when the lockupclutch embodying the friction lining 422 is engaged.

Each of the several passages 435 has an inlet 439 at the radially outerportion 422a and an outlet 440 at the radially inner portion 422b of thefriction lining 422. The illustrated nine passages 422 togetherconstitute a composite arcuate passage which extends along an arc ofnearly or exactly 360° when the friction lining 422 is bonded orotherwise affixed to the piston or to the other component which carriesa friction surface, e.g., to the piston 17 or to the wall 9 of thehousing 2 in the torque converter 3 of FIG. 1.

An advantage of an uninterrupted or continuous passage or of a compositepassage (such as the one including passages 435 of the type shown inFIG. 6) is that the fluid is compelled to flow along an elongated pathand to thereby withdraw large amounts of heat from the adjacent portionof the piston or the other component which carries a friction surface.This reduces the thermally induced stresses upon the piston and theadjacent component of the lockup clutch as well as upon the fluidcoolant.

The length and the configuration of the passages 435 in the frictionlining 422 are preferably selected in such a way that the resistance tothe flow of fluid coolant therein is satisfactory even under the mostdifficult or adverse circumstances of use of the lockup clutch and thetorque converter in which the clutch is put to use. In other words, evenif the fluid is being heated to a maximum permissible temperature, therate of fluid flow between the compartments at opposite sides of thepiston should not exceed that value at which the system pressure in thetorque converter is likely to collapse. It is preferred to select therate of fluid flow in the passages 435 in such a way that it is notunduly influenced by the temperature of the fluid, i.e., that the rateof fluid flow between the two compartments can or may fluctuatedepending upon variations of certain parameters of the torque converter,the prime mover which drives the torque converter and/or the unit orunits which receive torque from the torque converter, but should not bedependent, or should not be overly dependent, upon the fluctuations ofthe temperature of fluid coolant.

The nine illustrated passages 435 in the friction surface of thefriction lining 422 of FIG. 6 have identical dimensions and identicalshapes and are equidistant from each other when the friction lining isbonded to a frustoconical portion of the piston or to a frustoconicalportion of the adjacent wall of the housing or to a frustoconicalportion of a member corresponding to the member 24 in the torqueconverter 3 of FIG. 1. The number of discrete passages 422 can bereduced to less than nine or increased to ten or more, but is preferablynot less than three.

When bonded to a frustoconical surface (such as the left-hand side ofthe conical radially outer portion of the member 24 in the lockup clutch15 of FIG. 1), the split friction lining 422 preferably constitutes acircumferentially complete hollow conical frustum. In other words, thetwo end portions 436 and 437 of the friction lining 422 are then closelyor immediately adjacent each other or actually abut one another.

A friction lining of the type shown in FIG. 6 can be replaced by afriction lining which is assembled of two or more arcuate sections orsegments 438 of the character shown in FIG. 7. This reduces waste in thematerial of which the sections 438 are made. Each of the illustratedarcuate sections 438 is provided with a set of three identical passages435. The segments 438 are bonded or otherwise secured to the piston, tothe wall of the housing or to another member (such as 24) of the torqueconverter so that they jointly constitute a hollow frustoconicalfriction lining.

The manipulation of the arcuate sections 438 can be simplified byapplying an adhesive-coated foil to one side of the blank from which thesections are removed, e.g., in a stamping or another suitable machine.The application of such foil is facilitated because the one side of theblank is smooth, i.e., it need not be provided with passages 435 or withotherwise configurated and/or dimensioned passages. The provision ofcontinuous radially inner and radially outer portions 422a, 422b on thefriction lining 422 of FIG. 6 and of continuous radially inner andradially outer portions on the sections 438 of FIG. 7 also facilitatesthe manipulation of such friction lining or such sections prior to aswell as during bonding to a carrier such as the piston of the improvedlockup clutch.

It is clear that if, for example, the piston of the improved lockupclutch is to be provided with a friction lining of the type shown inFIG. 6 or 7, the piston must be provided with suitably distributedinlets (such as 26 or 226 or 326) to establish paths for the flow offluid coolant into the inlets 439 of the passages 435 in the frictionlining. Furthermore, it is necessary to establish paths (e.g., bores,holes, slots or the like) for the flow of fluid from the outlets 440 ofthe passages 435 into the channel of channels serving to cause the fluidto flow radially inwardly into the first compartment of the housing ofthe torque converter. Alternatively, the piston or another componentwhich carries a friction lining of the type shown in FIG. 6 or 7 can beprovided with grooves which receive fluid from the passages 435, i.e.,such carrier of the friction lining need not be provided with bores,holes or slots which extend all the way between the two sides of thecarrier. For example, the ports 228 in the piston 217 of FIG. 4 can beomitted if the left-hand side of the piston is provided with groovesreceiving fluid streams from the outlets 440 of passages 435 of the typeshown in FIG. 6 or 7. FIG. 5 shows, by broken lines, a groove 441 in theleft-hand side of the frustoconical portion of the piston 317; suchgroove is angularly offset relative to the respective inlet 326 anddirects fluid coolant into the compartment 318.

It is presently preferred to configurate the passages 435 in such a waythat each passage includes at least two turns which alter the directionof fluid flow from a direction toward the radially outer portion (suchas 422a) toward the radially inner portion (such as 422b) of therespective friction lining (such as 422). Each of the illustratedpassages 435 has six turns, i.e., a total of seven straight orsubstantially straight portions (depending upon whether the passages arezig-zag shaped or substantially zig-zag shaped, such as sinusoidal,snake-like or meandering). For example, each of the illustrated zig-zagshaped passages 435 can be replaced by a sinusoidal or snake-likepassage having a series of six concavo-convex portions.

FIG. 8 illustrates a portion of a torque converter wherein the piston417 of the lockup clutch carries a friction lining 422 identical with orresembling the friction lining of FIG. 6. The friction lining is bondedto the left-hand side of the frustoconical portion of the piston 417opposite the adjacent frustoconical portion of the wall forming part ofthe section 404 of the housing 402 of the torque converter. The section404 has an axially extending circumferential internal shoulder 402a atthe radially inner end of the illustrated passage 435. The shoulder 402abounds one side of the radially outermost portion of the channel formingpart of or leading into the compartment 418. In other words, theshoulder 402a is located opposite the outlets 440 of grooves 435 in thefriction lining 422.

In order to reduce the influence of the temperature and/or viscosity ofthe fluid coolant, as well as the influence of the pressure differentialbetween the two compartments in the housing of the torque converter,upon the rate of fluid flow between the two compartments, a furtherfeature of the present invention resides in the provision of one or moredevices constituting means for regulating the rate of fluid flow alongthe friction surfaces of the lockup clutch by taking into considerationthe variations of the aforementioned parameters, such as the temperatureand viscosity of the fluid and the difference between the pressures inthe two compartments of the housing of the torque converter. Theregulating means can vary the rate of fluid flow in dependency upon oneor more of the aforediscussed parameters.

The regulating means can comprise one or more adjustable valves 542 ofthe type shown in FIGS. 8a and 9. The illustrated valve 542 is carriedby the piston 517 and comprises a body or housing 543 located at thatside of the piston 517 which faces away from the friction lining 522. Tothis end, the body 543 comprises a short annular portion 544 which isreceived in a complementary bore or socket 545 of the piston 517. Forexample, the portion 544 can be a press fit in the socket 545.

As best shown in FIG. 9, the body 543 of the valve 542 defines a chamber552 for a reciprocable piston or plunger 546 (hereinafter called plungerto distinguish from the piston 517 of the lockup clutch). The plunger546 is provided with an axial extension 547 which is reciprocable in anopening 548 provided in a sleeve 550 which is installed in the body 543.Opening 548 constitutes the outlet of a path for the flow of fluidcoolant through the body 543. The rate of fluid flow through the body543 can be altered by changing the axial position of the plunger 546 inthe chamber 552. To this end, the extension 547 of the plunger 546 isconfigurated to ensure that the rate of fluid flow through one or moresubstantially axially parallel grooves 549 of the extension 547 isaltered in response to shifting of the plunger 546 toward or away fromthe bottom wall or end wall 554 of the body 543. The body 543 is furtherprovided with two or more tubular inlets 555 which admit the fluidcoolant into the groove or grooves 549 of the extension 547. It is alsopossible to configurate the surface bounding the opening 548 in thesleeve 550 in such a way that the rate of fluid flow from the valve 542into the respective passage 535 can be altered in a predictable mannerin response to axial displacement of the piston 546 in the cylinderchamber 552.

The sleeve 550 is a press fit or is otherwise securely held in the body543 and includes a smaller-diameter extension 551 in the chamber 552.The sleeve 550 and its extension 551 constitute a retainer for one endportion of a counterbalanced coil spring 553 which bears upon thelarger-diameter portion of the plunger 546 so that the plunger is urgedtoward the bottom end wall 554, i.e., in a direction to increase therate of fluid flow through the body 543.

The valve 542 increases the rate of fluid flow through its housing 543when the difference between the fluid pressures in the two compartmentsin the housing including the section 504 of FIG. 8a is relatively small.

The inlets 555 admit fluid from the second compartment of the housingincluding the section 504 into the inlet of the respective passage 535at the radially outer portion of the area 519 of frictional engagementbetween the friction lining 522 and the section 509 in the engagedcondition of the lockup clutch. It is also possible to install the valve542 and to configurate the piston 517 in such a way that the valve canadmit fluid coolant to two or more passages 535.

The configuration of the groove or grooves 549 in the extension 547 ofthe plunger 546 is such that the rate of fluid flow from the inlets 555to the opening 548 is reduced in response to shifting of the plunger 546in a direction to the left, i.e., so as to move the extension 547 deeperinto the opening 548. Furthermore, the characteristic of the spring 553is such that, in conjunction with appropriate shaping of the surface(s)surrounding the groove(s) 549, the valve 542 automatically regulates therate of fluid flow through the valve so that the rate is constant duringeach stage of operation of the torque converter. Furthermore, the valve542 renders it possible to ensure that the rate of fluid flow into therespective passage or passages 535 is at least substantially independentof the pressure differential in the compartments at opposite sides ofthe piston 517.

However, it is equally possible to design the valve 542 (e.g., byappropriate shaping of the surface(s) bounding the groove(s) 549 and/orby appropriate dimensioning of the cross-sectional area of the opening548 and/or by appropriate selection of the characteristic curve of thespring 553) in such a way that one can select any one of an array ofdifferent characteristic curves for the rate of fluid flow through thevalve. For example, the valve 542 can be designed in such a way that therate of fluid flow through the body 543 is gradually increased orgradually reduced in response to increasing difference between the fluidpressures in the two compartments of the housing of the torqueconverter. If desirable or necessary, the valve 542 or an analogousfluid flow regulating device can be designed and installed in such a waythat the flow of fluid in the passage(s) 535 is completely interruptedwhen the pressure differential between the two compartments rises to apredetermined value. However, at least in most instances, it isadvisable or sufficient to design the valve 542 or its equivalent insuch a way that the rate of fluid flow from the second compartment intothe passage(s) 535 is at least substantially constant, i.e., that it ispractically independent of fluctuations of pressure of fluid coolant inthe first and/or the second compartment, such as at the inlets 555 ofthe valve body 543. A valve which regulates the rate of fluid flow witha view to avoid any, or any appreciable, changes in response to changesof the difference between the fluid pressures in the two compartmentsexhibits the additional advantage that it can be readily designed andinstalled in such a way that the rate of fluid flow from the inlets 555to the opening 548 is at least substantially independent of fluctuationsof the temperature of the conveyed fluid.

FIG. 8a shows that the valve 542 is installed at the inlet 539 of thepassage 535 in the friction lining 522 which is bonded to the piston517.

FIG. 9a illustrates a modified fluid flow regulating valve 642 which canbe utilized in lieu of the valve 542. All that is necessary is to alterthe socket in the piston or another component of the torque converter sothat the body 643 of the valve 642 can be a press fit or is otherwisesecurely held therein. The valve 542 or 642 can also be used as asubstitute for the nozzle 326a which is shown in FIG. 5. The body 643defines a cylindrical chamber 652 for a reciprocable plunger 646. Thechamber 652 is a blind bore or hole in the body 643, and its open end ispartially sealed by a washer-like insert 650 defining a central opening650a constituting the inlet of the valve 642. A calibrated resilientelement 653, such as a coil spring, is installed in the cylinder chamber652 to react against the bottom end wall 654 and to bear upon theplunger 646 in order to urge the plunger toward the insert 650. FIG. 9ashows that the left-hand end face of the plunger 646 is provided with arecess 646a for a substantial number of convolutions of the spring 653.The plunger 646 divides the cylinder chamber 652 into a first section652a at the insert 650 and a second section 652b at the end wall 654.

The section 652a of the cylinder chamber 652 receives fluid coolant byway of the central opening 650a in the insert 650. The pressure of fluidentering the cylinder chamber section 652a corresponds to fluid pressurein the second compartment of the housing of the torque converter, i.e.,in that compartment which accommodates the turbine and the pump. Theleft-hand section 652b of the cylinder chamber 652 receives fluidthrough a flow restricting channel or orifice 657 in the plunger 646.The orifice 657 serves as a means for establishing a pressuredifferential Δp between the sections 652a and 652b of the cylinderchamber 652. The orifice 657 is in series with a regulating orifice 658which is provided in the valve body 643 and serves to regulate the rateof fluid flow into one or more passages depending upon the pressure offluid in the section 652a of the cylinder chamber 652. This is achievedin that, by properly selecting the cross-sectional area of theregulating orifice 658, one can select a predetermined value for thepressure differential Δp. As already pointed out hereinbefore, it isnormally advisable and desirable to regulate the rate of fluid flow insuch a way that it remains at least substantially constant. Theillustrated regulating orifice 658 is composed of a set of radiallyextending ports 648 in the body 643 of the valve 642. The effectivecombined cross-sectional area of the ports 648 is changed in response toaxial displacement of the plunger 646 in the cylinder chamber 652.

When the fluid pressure in the section 652a of the cylinder chamber 652rises, the plunger 646 is displaced in a direction to the left, asviewed in FIG. 9a, i.e., in a direction to stress the valve spring 653,so that the combined effective cross-sectional area of the ports 648 isreduced accordingly. This, in turn, entails a rise of fluid pressure inthe section 652b of the cylinder chamber 652 so that the pressuredifferential is altered in a direction to ensure that the rate of fluidflow from the cylinder chamber section 652b into the ports 648 matchesthe desired value. Each port 648 can discharge a fluid coolant into adiscrete passage or all of the ports 648 in the body 643 of the valve642 can admit fluid into the inlet of a single passage.

FIG. 10 illustrates a portion of a hydrokinetic torque converterincluding a lockup clutch 715 having a friction lining 722 bonded orotherwise affixed to the right-hand side of a substantiallyfrustoconical component 704a riveted (as at 760) or otherwise affixed tothe wall 709 of the section 704 of a composite housing which can beconstructed in the same way as the housing 2 of the torque converter 3shown in FIG. 1. The component 704a can be made of metallic sheetmaterial and the friction surface of its lining 722 confronts thefriction surface at the radially outermost portion of the piston 717.

The rivets 760 can constitute separately produced parts; however, and asactually shown in FIG. 10, each rivet 760 can also constitute a suitablydisplaced or depressed portion of the radially extending wall 709 of thehousing section 704. Each displaced portion of the wall 709 is receivedin a complementary socket or recess at the adjacent side of the wall704a.

The left-hand frustoconical surface of the wall 704a defines with theadjacent portion of the wall 709 an intermediate space 761 having asubstantially wedge-shaped cross-sectional outline. The space 761contains at least one fluid flow regulating valve 742 which is mountedon the wall 704a, and this space communicates with the secondcompartment of the chamber within the housing including the section 704.It can be said that the space 761 constitutes an extension of the secondcompartment.

The radially outermost portion of the wall 704a can be provided with anannularly arranged set of lugs, prongs or other protuberances which areanchored in the adjacent cylindrical portion of the housing section 704.Alternatively, the prongs, tongues or other protuberances can beprovided at the inner side of the housing section 704. In either event,the prongs of the wall 704a and/or of the housing section 704 aredistributed in such a way that they establish adequate paths for theflow of fluid from the second compartment of the housing into the space761 or from the major part of the second compartment into the smallerpart or space 761. The feature that the wall 704a is in engagement withthe adjacent portion of the housing section 704 ensures that the wall704a is highly unlikely to undergo any, or any appreciable, deformationwhich could result in undesirable axial shifting of the piston 717 underthe action of axial forces generated by the fluid flowing from thepassages 725 into one or more channels and thence into the firstcompartment.

The friction surface of the piston 717 is provided on a frustoconicalportion 730 which is adjacent the friction surface of the frictionlining 722 on the wall 704a. When the lockup clutch 715 is engaged,fluid coolant can flow from the space 761 into the valve or valves 742and thence into the passages 725. These passages are provided in thefriction lining 722. The valve 742 of FIG. 10 is or can be identicalwith the valve 542 of FIGS. 8a and 9 or with the valve 642 of FIG. 9a.

FIG. 11 shows a portion of still another hydrokinetic torque converterhaving a lockup clutch including a piston 817. A frustoconical portionof the piston 817 carries a friction lining 822 having passages 825 withinlets in communication with substantially axially parallel holes orbores 826 machined into or otherwise formed in the piston. A singlevalve 842 (corresponding to one of the valves described with referenceto FIGS. 8a, 9 and 9a) suffices to regulate the fluid pressure at theinlets of a plurality of identical or different passages 825 in thefriction surface of the lining 822. To this end, the outlet of the valve842 discharges fluid into an annular space 863 between the right-handside of the piston 817 and the left-hand side of a member 862 which iscarried by the piston. The inlets of the passages 825 communicate withthe annular space 863 by way of the respective bores or holes 826 in thepiston 817. FIG. 11 shows that the valve 842 is installed radiallyinwardly of the bores or holes 826, i.e., the fluid which enters thespace 863 between the member 862 and the piston 817 must flow radiallyoutwardly on its way into the inlets of the passages 825.

It is clear that the torque converter embodying the structure of FIG. 11can comprise two or more suitably distributed valves 842. Nevertheless,the provision of the member 862 and of the space 863 for fluid flowingtoward the passages 825 renders it possible to construct the lockupclutch in such a way that the number of valves 842 is less than thenumber of passages 825.

The just-discussed feature of the torque converter and lockup clutchembodying the structure of FIG. 11 can be relied upon in connection withthe construction of the torque converter 3 and lockup clutch 15 shown inFIG. 1. Thus, a fluid flow regulating valve (such as the valve 542 or642 of 742 or 842) can be installed on the piston 17 to supply fluidcoolant to the illustrated inlet 26a. Such inlet can supply fluidcoolant to all of the passages 25 in the friction lining 22.

It is desirable to construct and install the valve or valves 542, 642,742 or 842 in such a way that the influence of centrifugal forces on theregulating action of the valves is minimal, negligible or nil. This canbe readily achieved by utilizing relatively small and lightweightplungers in the bodies of the valves. The inertia of a lightweightplunger, especially a small or very small plunger, is sufficiently smallto ensure that the position of the plunger in its cylindrical chamber isnot influenced, or is not unduly influenced, by the centrifugal forcewhich develops when the housing of the torque converter is in actualuse. An additional undertaking involves such positioning of the axis ofthe plunger in the valve 542, 642, 742 or 842 that it is substantiallyparallel to the axis of the housing of the torque converter. This, too,reduces the likelihood that the axial position of the plunger wouldchange in response to the varying magnitude of centrifugal forces whenthe housing of the torque converter is rotated by a combustion engine oranother prime mover. The lightweight plunger can be made of a suitablemetallic material (such as aluminum) or of a suitable plastic material.The placing of the valve or valves as close to the axis of the housingas possible also contributes to a reduction of the influence ofcentrifugal forces upon the plunger. This can be seen in FIG. 11 whereinthe valve 842 is installed radially inwardly of the friction lining 822on the piston 817.

The valve or valves of the type described with reference to FIGS. 8a, 9,9a and 10 render it possible to regulate the rate of fluid flow betweenthe first and second compartments in such a way that the rate of fluidflow is not proportional to the square root of the difference betweenthe pressures of fluid coolant in the first and second compartments.

Hydrokinetic torque converters of the type disclosed in U.S. Pat. No.4,969,543 to Macdonald exhibit the drawback that the rate of fluid flowbetween the two compartments in the engaged condition of the lockupclutch is overly dependent upon the RPM of the housing of the torqueconverter. Thus, the rate of fluid flow is reduced considerably inresponse to increasing RPM of the housing. This is attributable to theaforediscussed dynamic or kinetic influences upon the conveyed fluid.Any undesirable and/or uncontrollable influences upon the rate of fluidflow are highly undesirable because they could alter the axial positionof the piston (and hence the maximum value of the torque transmittableby the lockup clutch) at a most inopportune time or stage of operationof the torque converter. It has been found that the influence of changesof the RPM of the housing upon the lockup clutch which embodies thepresent invention is negligible, and this is attributed to theaforediscussed feature that the fluid leaving the passages between thefriction surfaces of the lockup clutch is caused to flow at leastsubstantially radially inwardly on its way into the first compartment.It is now possible to ensure that, at a given system pressure in thetorque converter, the rate of fluid flow is low when the RPM of thehousing of the torque converter is low; this renders it possible toemploy a smaller and simpler pump.

FIG. 12 shows a portion of a ring-shaped or washer-like friction lining922 having a friction surface which is provided with meandering (e.g.,zig-zag shaped or sinusoidal or snake-like) passages 935. In theirentirety, the passages 935 extend in the circumferential direction ofthe friction lining 922. The configuration of the passages 935 issomewhat similar to that of the passages 435 in the friction liningsshown in FIGS. 6, 7 and 8. The width of the passages 935 is at leastsubstantially constant from the inlet to the outlet of each passage.Furthermore the cross-sectional outlines of the passages 935 arepreferably constant or at least substantially constant from end to end.

A difference between the passages 935 in the friction lining 922 of FIG.12 and the passages 435 of the friction lining 422 is that each passage922 is open at the radially outer portion 922a as well as at theradially inner portion 922b of the friction lining 922.

The passages 935 can be impressed into or otherwise formed in thefriction surface of the friction lining 922 during the making of thefriction lining, e.g., during the punching or stamping out of a largerblank. In other words, the passages 935 can be provided in the frictionlining 922 before the latter is bonded to a piston or to another part ofthe improved lockup clutch. However, it is equally possible to impressor to otherwise form the passages 935 during or subsequent to attachmentof the friction lining 922 to the piston or to another component ormember of the lockup clutch. Irrespective of whether the passages 935are formed prior to, during or subsequent to attachment of the frictionlining 922 to its carrier or support, such passages can be formed bysimply displacing some material at the friction surface of the frictionlining and/or by removing material from selected portions of thefriction surface. The same applies for all other types of frictionlinings which are or which should be utilized in the improved lockupclutch.

It has been found that the rate of fluid flow in the passages 935 of thefriction lining 922 is particularly satisfactory if each turn 946 or thesingle turn of a passage is flanked by two substantially or nearlystraight elongated portions or legs making an angle 945 of between 30°and 120°, preferably between 45° and 70°. The angle 945 which is shownin FIG. 12 equals or approximates 45°. Furthermore, each passage 935extending between the radially outer portion 939 and the radially innerportion 940 of the friction lining 922 is preferably configurated and/ororiented and/or dimensioned in such a way that a turbulent flow ofliquid coolant develops at the inlet and/or at the outlet (preferably atthe inlet as well as at the outlet) of each passage. It is advisable toselect the shape, the orientation and the dimensions of each passage 935(or at least a certain number of passages 935) in such a way that aturbulent fluid flow is established all the way from the inlet to theoutlet of the respective passage. This enhances the transfer of heatbetween such passage or passages and the adjacent components of thelockup clutch when the torque converter employing the lockup clutch isin use. For example, a turbulent flow of fluid in the passages 935 canbe established and maintained as a result of appropriate shaping of theturns 946 of the respective passages.

The feature that the passages 935 are rather close to each other andthat each such passage extends all the way or at least substantially allthe way between the radially outer portion 939 and the radially innerportion 940 of the friction lining also contributes to more satisfactoryremoval of heat from the friction lining as well as from the adjacentcomponents of the lockup clutch. The combined length of all passages 935in the friction lining 922 can be selected with a view to ensure arelatively high or a relatively low rate of withdrawal of heat from theneighboring components of the lockup clutch.

In order to achieve a desirable and predictable turbulence of the fluidcoolant in the passages 935, it is necessary or advisable to take intoconsideration the pressure differential between the inlets (at the outerportion 939) and the outlets (at the inner portion 940) of the passages.In a lockup clutch, such pressure differential corresponds to that ofthe pressure differential between the bodies of fluid coolant in thefirst and second compartments of the housing forming part of therespective torque converter, e.g., between the compartments 18 and 20 ofthe chamber 14 in the housing 2 of the torque converter 3 shown in FIG.1.

The withdrawal of heat from the friction lining 922 as well as from theadjoining components of the lockup clutch employing such friction liningcan be further enhanced by providing the radially outer portion 939and/or the radially inner portion 940 of the friction lining of FIG. 12with pockets 947 and 948 which can be obtained by depressing thecorresponding portions of the friction surface and/or by removingmaterial from such portions of the friction surface. As a rule, thepockets 947, 948 will be formed at the time of making the frictionlining 922 or at the time of making the passages 935, and preferably byresorting to the same procedure as that which is being resorted to forthe making of the passages 935.

The pockets 947 and 948 which are shown in FIG. 12 are triangularnotches in the respective marginal portions of the friction lining 922.The illustrated pockets can be used jointly with or replaced bysickle-shaped, semicircular and/or otherwise configurated pockets. Stillfurther, and as indicated by two radii 949 of curvature of the frictionlining 922, the inner pockets 948 need not be aligned with the outerpockets 947. FIG. 12 shows that the pockets 947 alternate with thepockets 948, as seen in the circumferential direction of the frictionlining 922. Of course, it is also possible to shape the friction surfaceof the friction lining in such a way that at least some of the pockets947 are in radial alignment with at least some of the pockets 948, thatindividual pockets 947 alternate with pairs or larger groups of pockets948 (as seen in the circumferential direction of the friction lining922), to provide pockets only in the radially outer portion 939 or toprovide pockets only in the radially inner portion 940.

FIG. 12 also shows that the illustrated inner pockets 948 alternate withthe radially inner turns 946 and that the radially outer pockets 947alternate with radially outer turns of the passages 935. When thefriction lining 922 is rotated by a piston or another component of thelockup clutch, the pockets 947 and 948 contain bodies of turbulent fluidor at least some of these pockets are filled with turbulent fluid. This,too, enhances the withdrawal of heat by the fluid coolant.

Still further, FIG. 12 shows that at least the majority of the pockets947 and 948 are in at least partial radial alignment with the adjoiningpassages 935. The provision of the passages 935 and pockets 947 and 948in the friction surface 950 of the friction lining 922 causes theremaining, intact portion of the friction surface 950 to assume asubstantially zig-zag shaped or a similar meandering, sinusoidal orsnake-like configuration.

The depth of passages 935 in the friction surface 950 of the frictionlining 922 or in the friction surface of a friction lining of the typeshown in FIGS. 6 to 8 can match or at least approximate the thickness ofthe respective friction lining. For example, the depth of passages 435or 935 can be such that they extend from the friction surface all theway to the other surface of the respective friction lining. This can bereadily achieved if the passages are formed subsequent to bonding of thefriction linings to the corresponding components of a lockup clutch.Furthermore, the passages 435 in the friction lining 422 of FIG. 6 canbe readily provided in the friction surface prior to bonding of thefriction lining to a piston or to another part of a lockup clutchbecause these passages do not extend all the way to the radially innerportion 422b or to the radially outer portion 422a of the frictionlining 422. In other words, the passages 435 do not divide therespective friction lining into a plurality of short arcuate sections.For example, the passages can be punched out from the blank of therespective friction lining. The same holds true for the pockets 947 and948 of the friction lining 922.

The provision of substantially meandering (such as zig-zag shaped)passages is desirable and advantageous for several reasons, for example,because the path or paths for the flow of liquid coolant in the frictionsurface of the friction lining are lengthened as well as because thefluid is caused to repeatedly flow back and forth between the radiallyinner and the radially outer portions of the friction lining. It hasbeen found that it is advisable to provide each passage 435 or 935 withat least two turns (such as the turns 946 shown in FIG. 12) andpreferably with four or more turns.

An advantage of one-piece friction linings (such as 422 and 922) is thatthey can be readily converted into hollow frustoconical bodies which canbe bonded to the frustoconical surface of a piston, housing or othercomponent of the lockup clutch in a simple and time-saving manner. Onthe other hand, a friction lining which is assembled of two or morearcuate sections (such as the friction lining sections 438 shown in FIG.7) exhibits the advantage that the sections can be punched out orotherwise separated from a large sheet-like blank of friction liningmaterial with a minimum of waste. As already mentioned above, one sideof the blank which is to be converted into friction linings 422 or 922,or into friction lining sections 438, can be provided with a film ofadhesive-coated material; this facilitates the manipulation of thefriction linings prior and during bonding to the pistons or othercomponents of lockup clutches. The provision of such films isparticularly advantageous if the passages are of the type shown in FIG.12, i.e., when the making of passages 935 involves the breaking up of asubstantially circular blank into a number of arcuate portions each ofwhich is provided with a passage 935 and a number of pockets 947 and948.

Friction linings 422 of the type shown in FIG. 6 are preferred in manyinstances because the making of passages 435 does not involve or entaila subdivision of an arcuate blank into a set of discrete arcuateportions or sections. This is particularly advantageous in connectionwith bonding of such a friction lining to a piston or the like. Thus, aone-piece friction lining is more likely to be bonded to a component ofa lockup clutch in such a way that its passages and pockets (if any) aredistributed and oriented in a manner to ensure highly satisfactory flowof fluid coolant along the friction surfaces of the lockup clutch.

It is further within the purview of the invention to provide suitablydistributed passages (e.g., of the type shown in FIGS. 6 to 8 or in FIG.12) in a component other than the friction lining of a lockup clutch.For example, such passages can be machined into the friction surface 21of the wall 9 shown in FIG. 1, and the passages in the friction surface21 can be provided in addition to or in lieu of the passages 25 in thefriction lining 22 on the piston 17. If the wall 9 is provided with aset of suitably distributed passages, they are or can be machined in thefriction surface 21 by removing material from the housing section 4 in asuitable machine tool or in any other known manner.

In accordance with one presently preferred embodiment of the invention,the ratio of the thickness of a friction lining (such as 22) to thedepth of the passages (such as 25) therein can be in the range ofbetween 1.3 and 2.7. As used therein, the term depth is intended todenote the average depth of a passage in the friction lining. The actualdepth of a passage (such as 25, 435 or 935) can be in the range ofbetween 0.2 mm and 0.8 mm, preferably between 0.3 mm and 0.6 mm. As arule, or at least in many instances, the depth of a passage will beconstant from end to end, for example, because the flow of fluid thereinis more predictable and also for convenience of mass production offriction linings. However, it can happen that, in certain hydrokinetictorque converters, the piston or another component of the lockup clutchwill be configurated in such a way that the the width and/or depth ofits passages varies in or counter to the direction of fluid flowtherein. FIG. 11a shows the structure of FIG. 11 with a passage 1000 ofvarying depth provided in the friction lining 822. The character 1001denotes a portion of the friction lining 822 adjacent the passage 1000.

The resort to zig-zag shaped or similar passages in the friction surfaceof a friction lining or in the friction surface of another component ofthe improved lockup clutch automatically entails at least somethrottling of the fluid flow from the inlet toward the outlet of suchpassage. Referring again to FIGS. 6 to 8 and 12, the length of eachstraight portion of a passage 435 or 935 can be in the range of between10 mm and 40 mm, and the width of such passages can be between 3 mm and10 mm.

In order to ensure that the rate of fluid flow in the passages of afriction lining or in the friction surface other than that of a frictionlining will at most equal or approximate ten liters per minute (suchrate has been found to be quite satisfactory for adequate cooling ofselected parts of a lockup clutch which is constructed and operated inaccordance with the present invention), and assuming that the fluidpressure at that side of the piston which faces the turbine of thetorque converter is to be in the range of 5 bar, the depth of thepassages (such as 435) can equal or approximate 3 mm. The overall numberof zig-zag shaped or similar passages in a friction lining or in a partother than a friction lining of the improved lockup clutch is preferablynot less than four and need not exceed twelve. It is preferred to ensureat least substantially uniform distribution of passages in the entirefriction surface, be it that of a friction lining or of anothercomponent of the lockup clutch. The spacing between two neighboringturns (such as 946 in the friction lining 922 of FIG. 12) at theradially outer portion (922a) and/or at the radially inner portion(922b) of the friction surface in relation to the width of that portionof a friction surface (950) which is provided with passages can be inthe range of between 0.6 and 1.3, preferably between 0.8 and 1.1.

The depth of the pockets 947 and/or 948 can match or at leastapproximate the depth of the respective passages (935 in FIG. 12).However, it is equally possible, and often preferred, to provide afriction lining with pockets which extend all the way between the twosides of the friction lining, even if the depth of the passages is lessthan the thickness of the friction lining because the making of suchpockets is simpler than the making of pockets extending from thefriction surface toward but short of the other surface of the frictionlining.

The ratio of that area of the friction surface of a friction liningwhich remains intact upon completion of the making of passages to theremaining area of the friction lining is preferably between about 0.7and 1.8, most preferably between 1 and 1.5. Thus, and referring to thefriction lining 922 of FIG. 12, the ratio of that portion of thefriction surface 950 which has been removed to form the passages 935(with or without the portion which has been removed to form the pockets947 and 948) to the area of the remaining part of the friction surface950 is preferably within the aforementioned range. This has been foundto be quite satisfactory to ensure adequate cooling of the frictionlining and of the neighboring parts of the improved lockup clutchwithout overheating of the fluid coolant.

The improved cooling action of the fluid which can enter the pockets(such as 947 and/or 948) of a friction lining (such as 922) isattributable to the establishment of a so-called drag flow whichdevelops along the radially inner and radially outer portions of arotating friction lining. It has been found that the cooling effect ofpockets in the one and/or the other marginal portion of a rotatingfriction lining is particularly satisfactory if the radially outer inletportion of a pocket trails the radially outer outlet portion of thepocket, as seen in the direction of rotation of the friction lining. Thecooling action upon the friction lining and upon the neighboring partsof the improved lockup clutch can be further enhanced by orienting thepassages in its friction surface in such a way that the fluid coolanttherein flows in the same direction as the aforementioned drag flowsalong the marginal portions when the friction lining is caused to rotateabout the axis of the housing forming part of the hydrokinetic torqueconverter embodying the improved lockup clutch. The drag flow along themarginal portions of a rotating friction lining which is bonded to thepiston of the lockup clutch or to a member (such as the member 24 inFIG. 1) which rotates with the piston is caused by that constituent ofthe lockup clutch which carries the other friction surface. Withreference to the embodiment of FIG. 1, the aforementioned constituent isthe wall 9 of the housing section 4.

When the two friction surfaces of the lockup clutch are free to sliderelative to each other while the lockup clutch transmits torque from thehousing to the turbine of the torque converter, the RPM of the housingexceeds the RPM of the friction lining if the latter is provided on thepiston or on a member which shares all angular movements of the piston.Therefore, the friction surface of the housing accelerates the fluid inthe passages of the adjacent friction lining. It has been found that theaccelerating action of the housing (such as the housing 2 in FIG. 1)upon the fluid in the passages of the friction lining (such as thepassages 25 in the friction lining 22 of FIG. 1) is greatly reduced ordoes not develop at all if the passages are dimensioned, oriented anddistributed in a manner as described with reference to the illustratedembodiments of the present invention. Thus, the influence of the RPM ofthe housing of the torque converter upon the magnitude of torque whichcan be transmitted by the lockup clutch is negligible (especially whencompared to the influence of the housing upon the friction lining of aconventional lockup clutch) or nil. The situation is analogous if thefriction lining is carried by the housing and its friction surfaceconfronts the friction surface of a metallic piston. Still further, thesame advantages or similar advantages can be achieved if the passagesare provided directly in the friction surface (such as 21) of a housing(such as 2) or in the friction surface of a metallic pressure plate(such as the piston 17 without the friction lining 22). This, in turn,renders it possible to employ a friction lining without any passagestherein. For example, if the passages 25 are provided in the housing 2of FIG. 1 instead of in the friction lining 22, such friction lining canbe replaced with a friction lining having an uninterrupted frictionsurface free of passages and/or pockets, or a friction surface providedwith pockets and/or passages whose distribution does not correspond tothat shown in FIG. 6, 7 or 12. Even though some turbulence in the fluidstreams flowing in the passages in a distribution as describedhereinbefore will or can develop due to the establishment of a pressuredifferential between the fluid bodies in the first and secondcompartments when the torque converter is in use, such turbulence can beenhanced (with attendant improvement of the heat withdrawing action ofthe fluid) if the passages in a friction lining or in the frictionsurface of a metallic part (such as the housing 2 or the piston 17 ofthe structure shown in FIG. 1) are dimensioned, oriented and distributedin a manner as described, for example, with reference to FIGS. 6, 7 and12. In other words, it is possible to select the configuration, thedimensions and/or the orientation of the passages for the expresspurpose of ensuring that, in addition to other important advantages, thepassages ensure the development of pronounced turbulence at the inlet,at the outlet or along the full length of each passage or of a certainnumber of passages.

The provision of one or more valves of the type shown in and describedwith reference to FIGS. 8a, 9, 9a, 10 and 11 constitutes an optional buthighly desirable and advantageous feature of the improved lockup clutchand of the torque converter embodying such lockup clutch. The flowregulating action of each such valve can be influenced by one or morevariable parameters of the fluid coolant, of the lockup clutch, of thetorque converter, of the prime mover for the housing of the torqueconverter and/or of the unit or units receiving torque from the turbineof the torque converter. For example, the only variable parameter or oneof the variable parameters which can influence the rate of fluid flowthrough one or more valves can constitute the temperature of the fluidcoolant, the RPM of the prime mover, the RPM of the turbine (i.e., theRPM of the rotary input element of a unit, such as a transmission,receiving torque from the torque converter) and/or particularly thepressure differential between the bodies of fluid in the first andsecond compartments. The valve or valves can regulate the rate of fluidflow between the two friction surfaces of the lockup clutch in such away that, when the lockup clutch is engaged, the rate of fluid flowbetween the two friction surfaces is at least substantially constantwithin the entire operating range of the torque converter. However, andas already discussed hereinbefore, it is also possible to select therate of fluid flow in such a way that it is a function of the extent ofslippage of the two friction surfaces relative to each other in theengaged condition of the lockup clutch. This is tantamount to aregulation of the rate of fluid flow depending upon the amount ofadditional heat which develops as a result of slippage of the twofriction surfaces relative to each other. Highly satisfactory resultscan be achieved by employing one or more valves which regulate the rateof fluid flow depending upon the variations of pressure differentialbetween the bodies of fluid coolant in the first and secondcompartments.

The valve or valves can be installed at the inlets or at the outlets ofthe passages or at the inlet(s) of the channel(s) serving to receivefluid from the passages. Still further, it is possible to install thevalves in the passages between the inlets and the outlets of therespective passages.

Still further, it is possible to employ solenoid operated valves in lieuof the valves which are shown in FIGS. 8a, 9, 9a, 10 and 11.

The improved hydrokinetic torque converter and its lockup clutch aresusceptible of numerous additional modifications without departing fromthe spirit of the present invention. For example, certain features ofthe illustrated and described embodiments of the novel torque converterand/or of its lockup clutch can be combined or interchanged. Inaddition, numerous features of the aforedescribed torque converter andof its lockup clutch are believed to constitute patentable innovationseven if they are embodied in conventional torque converters and/orlockup clutches. This applies, for example, to the making andconfiguration and utilization of the aforedescribed friction linings andtheir passages, to the utilization of the aforediscussed fluid flowregulating valves or analogous flow regulating means in conjunction withor without the friction linings, and to the construction and mounting ofthe piston and certain other components and/or members of the lockupclutch. Last but not least, it is within the scope of the invention toconstruct and assemble a power train, including a prime mover (such as acombustion engine in a motor vehicle), one or more driven units (e.g., atransmission or a differential in a motor vehicle) and the improvedlockup clutch or bypass clutch in combination with the improved torqueconverter or with a conventional torque converter to arrive at apatentable power train.

The disclosures of all of the aforementioned U.S. patents, pendingpatent applications and the corresponding U.S. patents and/or patentapplications are incorporated herein by reference.

Without further analysis, the foregoing will so fully reveal the gist ofthe present invention that others can, by applying current knowledge,readily adapt it for various applications without omitting featuresthat, from the standpoint of prior art, fairly constitute essentialcharacteristics of the generic and specific aspects of theabove-outlined contribution to the art and, therefore, such adaptationsshould and are intended to be comprehended within the meaning and rangeof equivalence of the appended claims.

What is claimed is:
 1. A hydrokinetic torque converter comprising ahousing defining a fluid-containing chamber and being rotatable about apredetermined axis; a pump in said housing; a turbine in said housing;and an engageable and disengageable lockup clutch in said housing, saidclutch comprising an annular piston dividing said chamber into first andsecond compartments, at least one first friction surface carried by saidpiston, a component provided with at least one second friction surfacecomplementary to and contacting said at least one first friction surfacein the engaged condition of said clutch, said friction surfaces beingdisposed at a predetermined first radial distance from said axis and oneof said compartments being disposed between said piston and saidcomponent at a second radial distance from said axis, said second radialdistance being less than said first radial distance, and elongatedpassages provided in at least one of said piston and said component andsaid friction surface at said first radial distance from said axis toestablish a path for the flow of fluid from the other of saidcompartments toward said one compartment in the engaged condition ofsaid clutch, at least one of said passages being at least substantiallyzig-zag shaped and at least one of said passages having a substantiallyconstant cross-section.
 2. A hydrokinetic torque converter comprising ahousing defining a fluid-containing chamber and being rotatable about apredetermined axis; a pump in said housing; a turbine in said housing;and an engageable and disengageable lockup clutch in said housing, saidclutch comprising an annular piston dividing said chamber into first andsecond compartments, at least one first friction surface carried by saidpiston, a component provided with at least one second friction surfacecomplementary to and contacting said at least one first friction surfacein the engaged condition of said clutch, said friction surfaces beingdisposed at a predetermined first radial distance from said axis and oneof said compartments being disposed between said piston and saidcomponent at a second radial distance from said axis, said second radialdistance being less than said first radial distance, and passagesprovided in at least one of said piston and said component and saidfriction surface at said first radial distance from said axis toestablish a path for the flow of fluid from the other of saidcompartments toward said one compartment in the engaged condition ofsaid clutch, at least one of said passages being at least substantiallyzig-zag shaped and at least one of said passages being elongated andhaving an inlet and an outlet, said inlet and said outlet extendingsubstantially radially of said axis.
 3. A hydrokinetic torque convertercomprising a housing defining a fluid-containing chamber and beingrotatable about a predetermined axis; a pump in said housing; a turbinein said housing; and an engageable and disengageable lockup clutch insaid housing, said clutch comprising an annular piston dividing saidchamber into first and second compartments, at least one first frictionsurface carried by said piston, a component provided with at least onesecond friction surface complementary to and contacting said at leastone first friction surface in the engaged condition of said clutch, saidfriction surfaces being disposed at a predetermined first radialdistance from said axis and one of said compartments being disposedbetween said piston and said component at a second radial distance fromsaid axis, said second radial distance being less than said first radialdistance, and passages provided in at least one of said piston and saidcomponent and said friction surface at said first radial distance fromsaid axis to establish a path for the flow of fluid from the other ofsaid compartments toward said one compartment in the engaged conditionof said clutch, at least one of said passages being at leastsubstantially zig-zag shaped and at least one of said passages havingtwo portions inclined relative to and making with each other an angle ofbetween 30° and 120 °.
 4. A hydrokinetic torque converter comprising ahousing defining a fluid-containing chamber and being rotatable about apredetermined axis; a pump in said housing; a turbine in said housing;and an engageable and disengageable lockup clutch in said housing, saidclutch comprising an annular piston dividing said chamber into first andsecond compartments, at least one first friction surface, a componentprovided with at least one second friction surface complementary to andcontacting said at least one first friction surface in the engagedcondition of said clutch, said friction surfaces being disposed at afirst radial distance from said axis and one of said compartments beingdisposed between said piston and said component at a second radialdistance from said axis, said second radial distance being less thansaid first radial distance, and passages provided in at least one ofsaid piston, said at least one first friction surface, said at least onesecond friction surface and said component at said first radial distancefrom said axis to establish a path for the flow of fluid from the otherof said compartments toward said one compartment in the engagedcondition of said clutch, each of said passages extending between afluid inlet and a fluid outlet, with a variable direction defined by aradial component and a circumferential component, and each passagehaving at least one change of direction at which the radial componentsat opposite sides of the respective change of direction are oppositelydirected.
 5. The converter of claim 4, wherein each of said passages hasa plurality of changes of direction.
 6. The torque converter of claim 4,wherein each of said passages has a change of direction adjacent aninner edge of a friction lining of said clutch.
 7. The torque converterof claim 4, wherein each of said passages has a change of directionadjacent an outer edge of a friction lining of said clutch.
 8. Theconverter of claim 4, wherein each inlet and each outlet is associatedwith a single passage.
 9. The torque converter of claim 4, wherein saidpassages overlap radially.
 10. A hydrokinetic torque convertercomprising a housing rotatable about a predetermined axis and arrangedto confine a supply of fluid; and an engageable and disengageable lockupclutch including a piston disposed in said housing and movable in thedirection of said axis toward and away from a portion of said housing, afriction lining disposed between said piston and said portion of saidhousing and having a friction surface provided with channels definingpaths for the flow of said fluid from a chamber in said housing, saidfriction surface having radially inner and radially outer marginalportions and said channels extending between said marginal portions in acircumferential direction of said piston and at varying distances fromsaid axis, each of said channels including at least one turn whichchanges the direction of fluid flow in the respective channel so thatthe fluid flowing in a portion of the channel upstream of the respectiveturn has a first radial component and the fluid flowing in a portion ofthe channel downstream of the respective turn has a second radialcomponent counter to said first radial component.